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  • Introduction
  • Let's start
  • Decide if/else
  • Loop and loop
  • Decide and loop
  • My functions
  • Pre-processor
  • Enjoy with files
  • Dynamic memory
  • Storage classes

Arrays in C

In simple English, an array is a collection.

In C also, it is a collection of similar type of data which can be either of int, float, double, char (String), etc. All the data types must be same. For example, we can't have an array in which some of the data are integer and some are float.

array in c

Suppose we need to store marks of 50 students in a class and calculate the average marks. So, declaring 50 separate variables will do the job but no programmer would like to do so. And there comes array in action.

How to declare an array

datatype   array_name [ array_size ] ;

For example, take an array of integers 'n'.

n[ ] is used to denote an array 'n'. It means that 'n' is an array.

array of integers in C

We need to give the size of the array because the complier needs to allocate space in the memory which is not possible without knowing the size. Compiler determines the size required for an array with the help of the number of elements of an array and the size of the data type present in the array.

Here 'int n[6]' will allocate space to 6 integers.

We can also declare an array by another method.

int n[ ] = {2, 3, 15, 8, 48, 13};

In this case, we are declaring and assigning values to the array at the same time. Here, there is no need to specify the array size because compiler gets it from { 2,3,15,8,48,13 } .

Index of an Array

Every element of an array has its index. We access any element of an array using its index.

Pictorial view of the above mentioned array is:

0, 1, 2, 3, 4 and 5 are indices. It is like they are identity of 6 different elements of an array. Index always starts from 0. So, the first element of an array has a index of 0.

We access any element of an array using its index and the syntax to do so is:

array_name[index]

For example, if the name of an array is 'n', then to access the first element (which is at 0 index), we write n[0] .

Here, n[0] is 2 n[1] is 3 n[2] is 15 n[3] is 8 n[4] is 48 n[5] is 13

elements of array in C

n[0] , n[1] , etc. are like any other variables we were using till now i.e., we can set there value as n[0] = 5; like we do with any other variables ( x = 5; , y = 6; , etc.).

Assigning Values to Array

By writing int n[ ]={ 2,4,8 }; , we are declaring and assigning values to the array at the same time, thus initializing it.

But when we declare an array like int n[3]; , we need to assign values to it separately. Because 'int n[3];' will definitely allocate space of 3 integers in memory but there are no integers in that space.

To initialize it, assign a value to each of the elements of the array.

n[0] = 2; n[1] = 4; n[2] = 8;

It is just like we are declaring some variables and then assigning values to them.

int x,y,z; x=2; y=4; z=8;

Thus, the first way of assigning values to the elements of an array is by doing so at the time of its declaration.

int n[ ]={ 2,4,8 };

And the second method is declaring the array first and then assigning values to its elements.

int n[3]; n[0] = 2; n[1] = 4; n[2] = 8;

You can understand this by treating n[0] , n[1] and n[2] as similar to different variables you used before.

Just like variable, array can be of any other data type also.

float f[ ]= { 1.1, 1.4, 1.5};

Here, 'f' is an array of floats.

First, let's see the example to calculate the average of the marks of 3 students. Here, marks[0] represents the marks of the first student, marks[1] represents marks of the second and marks[2] represents marks of the third student.

Here you just saw a working example of array, we treated elements of the array in an exactly similar way as we had treated normal variables. &marks[0], &marks[1] and &marks[2] represent the addresses of marks[0], marks[1] and marks[2] respectively.

We can also use for loop as done in the next example.

The above code was just to make you familiar with using loops with an array because you will be doing this many times later.

The code is simple, 'i' and 'j' start from 0 because the index of an array starts from 0 and goes up to 9 (for 10 elements). So, 'i' and 'j' goes up to 9 and not 10 ( i<10 and j<10 ). So, in the code n[i] will be n[1], n[2], ...., n[9] and things will go accordingly.

Suppose we declare and initialize an array as

int n[5] = { 12, 13, 5 };

This means that n[0]=12, n[1]=13 and n[2]=5 and rest all elements are zero i.e. n[3]=0 and n[4]=0.

int n[5]; n[0] = 12; n[1] = 13; n[2] = 5;

In the above code, n[0], n[1] and n[2] are initialized to 12, 13 and 5 respectively. Therefore, n[4] and n[5] are both 0.

Pointer to Arrays

Till now, we have seen how to declare and initialize an array. Now, we will see how we can have pointers to arrays too. But before starting, we are assuming that you have gone through Pointers from the topic Point Me . If not, then first read the topic Pointers and practice some problems from the Practice section .

As we all know that pointer is a variable whose value is the address of some other variable i.e., if a variable 'y' points to another variable 'x', it means that the value of the variable 'y' is the address of 'x'.

Similarly, if we say that a variable 'y' points to an array 'n', it would mean that the value of 'y' is the address of the first element of the array i.e. n[0]. It means that the pointer of an array is the pointer of its first element.

If 'p' is a pointer to array 'age', means that p (or age) points to age[0].

int age[50]; int *p; p = age;

The above code assigns 'p' the address of the first element of the array 'age'.

address of an array in C

Now, since 'p' points to the first element of array 'age', '*p' is the value of the first element of the array.

So, *p is age[0], *(p+1) is age[1], *(p+2) is age[2].

Similarly, *age is age[0] (value at age), *(age+1) is age[1] (value at age+1), *(age+2) is age[2] (value at age+2) and so on.

That's all in pointer to arrays.

Now let's see some examples.

As 'p' is pointing to the first element of array, so, *p or *(p+0) represents the value at p[0] or the value at the first element of 'p'. Similarly, *(p+1) represents value at p[1]. And *(p+3) and *(p+4) represents p[3] and p[4] respectively. So accordingly, things were printed.

The above example sums up the above concepts. Now, let's print the address of the array and also individual elements of the array.

As you have noticed that the address of the first element of n and p are same and this means I was not lying! You can print other elements' addresses by using (p+1), (p+2) and (p+3) also.

Let's pass whole Array in Function

In C, we can pass an element of an array or the full array as an argument to a function.

Let's first pass a single array element to function.

Passing an entire Array in a Function

We can also pass the entire array to a function by passing array name as the argument. Yes, the trick is that we will pass the address of an array, that is the address of the first element of the array. Thus by having the pointer of the first element, we can get the entire array as we have done in examples above.

passing array to function

Let's see an example to understand it.

average(float a[]) → It is the function that is taking an array of float. And rest of the body of the function is performing accordingly.

b = average(n) → One thing you should note here is that we passed 'n'. And as discussed earlier, 'n' is the pointer to the first element or pointer to the array n[] . So, we have actually passed the pointer.

In the above example in which we calculated the average of the values of the elements of an array, we already knew the size of the array i.e. 8.

Suppose we are taking the size of the array from the user. In that case, the size of the array is not fixed. Here, we need to pass the size of array as the second argument to the function.

The code is similar to the previous one except that we passed the size of array explicitly - float average(float a[], int size ) .

We can also pass an array to a function using pointers. Let's see how.

In the above example, the address of the array i.e. address of n[0] is passed to the formal parameters of the function.

display(int *p) → This means that function 'display' is taking a pointer to an integer.

Now we passed the pointer of an integer i.e. pointer of the array n[] - 'n' as per the demand of our function 'display'.

Since 'p' is the address of the array n[] in the function 'display' i.e., address of the first element of the array (n[0]), therefore *p represents the value of n[0]. In the for loop in function, p++ increases the value of p by 1. So, when i=0, the value of *p gets printed. Then p++ increases *p to *(p+1) and in the second loop, the value of *(p+1) i.e. n[1] also gets printed. This loop continues till i=7 when the value of *(p+7) i.e. n[7] gets printed.

passing array to function

What if arrays are 2 dimensional?

Yes, 2-dimensional arrays also exist and are generally known as matrix . These consist of rows and columns.

Before going into its application, let's first see how to declare and initialize a 2D array.

Declaration of 2D Array

Similar to one-dimensional array, we define a 2-dimensional array as below.

int a[2][4];

Here, 'a' is a 2D array of integers which consists of 2 rows and 4 columns .

Now let's see how to initialize a 2-dimensional array.

Assigning Values to a 2 D Array

Same as in one-dimensional array, we can assign values to the elements of a 2-dimensional array in 2 ways as well.

In the first method, just assign a value to the elements of the array. If no value is assigned to any element, then its value is assumed to be zero.

Suppose we declared a 2-dimensional array a[2][2] . Now, we need to assign values to its elements.

int a[2][2]; a[0][0]=1; a[0][1]=2; a[1][0]=3; a[1][1]=4;

The second way is to declare and assign values at the same time as we did in one-dimensional array.

int a[2][3] = { 1, 2, 3, 4, 5, 6 };

Here, value of a[0][0] is 1, a[0][1] is 2, a[0][2] is 3, a[1][0] is 4, a[1][1] is 5 and a[1][2] is 6.

We can also write the above code as:

int a[2][3] = {       {1, 2, 3},       {4, 5, 6 }     };

Let's consider different cases of assigning values to an array at the time of declaration.

int a[2][2] = { 1, 2, 3, 4 }; /* valid */ int a[ ][2] = { 1, 2, 3, 4 }; /* valid */ int a[2][ ] = { 1, 2, 3, 4 }; /* invalid */ int a[ ][ ] = { 1, 2, 3, 4 }; /* invalid */

Why use of 2 D Array

Suppose we have 3 students each studying 2 subjects (subject 1 and subject 2) and we have to display the marks in both the subjects of the 3 students. Let's input the marks from the user.

This is something like

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C Programming/Pointers and arrays

A pointer is a value that designates the address (i.e., the location in memory), of some value. Pointers are variables that hold a memory location.

There are four fundamental things you need to know about pointers:

  • How to declare them (with the address operator ' & ': int *pointer = &variable; )
  • How to assign to them ( pointer = NULL; )
  • How to reference the value to which the pointer points (known as dereferencing , by using the dereferencing operator ' * ': value = *pointer; )
  • How they relate to arrays (the vast majority of arrays in C are simple lists, also called "1 dimensional arrays", but we will briefly cover multi-dimensional arrays with some pointers in a later chapter ).

Pointers can reference any data type, even functions. We'll also discuss the relationship of pointers with text strings and the more advanced concept of function pointers.

  • 1 Declaring pointers
  • 2 Assigning values to pointers
  • 3 Pointer dereferencing
  • 4 Pointers and Arrays
  • 5 Pointers in Function Arguments
  • 6 Pointers and Text Strings
  • 7.1 Practical use of function pointers in C
  • 8 Examples of pointer constructs
  • 10 External Links

Declaring pointers [ edit | edit source ]

Consider the following snippet of code which declares two pointers:

Lines 1-4 define a structure . Line 8 declares a variable that points to an int , and line 9 declares a variable that points to something with structure MyStruct. So to declare a variable as something that points to some type, rather than contains some type, the asterisk ( * ) is placed before the variable name.

In the following, line 1 declares var1 as a pointer to a long and var2 as a long and not a pointer to a long. In line 2, p3 is declared as a pointer to a pointer to an int.

Pointer types are often used as parameters to function calls. The following shows how to declare a function which uses a pointer as an argument. Since C passes function arguments by value, in order to allow a function to modify a value from the calling routine, a pointer to the value must be passed. Pointers to structures are also used as function arguments even when nothing in the struct will be modified in the function. This is done to avoid copying the complete contents of the structure onto the stack. More about pointers as function arguments later.

Assigning values to pointers [ edit | edit source ]

So far we've discussed how to declare pointers. The process of assigning values to pointers is next. To assign the address of a variable to a pointer, the & or 'address of' operator is used.

Here, pPointer will now reference myInt and pKeyboard will reference dvorak.

Pointers can also be assigned to reference dynamically allocated memory. The malloc() and calloc() functions are often used to do this.

The malloc function returns a pointer to dynamically allocated memory (or NULL if unsuccessful). The size of this memory will be appropriately sized to contain the MyStruct structure.

The following is an example showing one pointer being assigned to another and of a pointer being assigned a return value from a function.

When returning a pointer from a function, do not return a pointer that points to a value that is local to the function or that is a pointer to a function argument. Pointers to local variables become invalid when the function exits. In the above function, the value returned points to a static variable. Returning a pointer to dynamically allocated memory is also valid.

Pointer dereferencing [ edit | edit source ]

To access a value to which a pointer points, the * operator is used. Another operator, the -> operator is used in conjunction with pointers to structures. Here's a short example.

The expression bb->m_aNumber is entirely equivalent to (*bb).m_aNumber . They both access the m_aNumber element of the structure pointed to by bb . There is one more way of dereferencing a pointer, which will be discussed in the following section.

When dereferencing a pointer that points to an invalid memory location, an error often occurs which results in the program terminating. The error is often reported as a segmentation error. A common cause of this is failure to initialize a pointer before trying to dereference it.

C is known for giving you just enough rope to hang yourself, and pointer dereferencing is a prime example. You are quite free to write code that accesses memory outside that which you have explicitly requested from the system. And many times, that memory may appear as available to your program due to the vagaries of system memory allocation. However, even if 99 executions allow your program to run without fault, that 100th execution may be the time when your "memory pilfering" is caught by the system and the program fails. Be careful to ensure that your pointer offsets are within the bounds of allocated memory!

The declaration void *somePointer; is used to declare a pointer of some nonspecified type. You can assign a value to a void pointer, but you must cast the variable to point to some specified type before you can dereference it. Pointer arithmetic is also not valid with void * pointers.

Pointers and Arrays [ edit | edit source ]

Up to now, we've carefully been avoiding discussing arrays in the context of pointers. The interaction of pointers and arrays can be confusing but here are two fundamental statements about it:

  • A variable declared as an array of some type acts as a pointer to that type. When used by itself, it points to the first element of the array.
  • A pointer can be indexed like an array name.

The first case often is seen to occur when an array is passed as an argument to a function. The function declares the parameter as a pointer, but the actual argument may be the name of an array. The second case often occurs when accessing dynamically allocated memory.

Let's look at examples of each. In the following code, the call to calloc() effectively allocates an array of struct MyStruct items.

Pointers and array names can pretty much be used interchangeably; however, there are exceptions. You cannot assign a new pointer value to an array name. The array name will always point to the first element of the array. In the function returnSameIfAnyEquals , you could however assign a new value to workingArray, as it is just a pointer to the first element of workingArray. It is also valid for a function to return a pointer to one of the array elements from an array passed as an argument to a function. A function should never return a pointer to a local variable, even though the compiler will probably not complain.

When declaring parameters to functions, declaring an array variable without a size is equivalent to declaring a pointer. Often this is done to emphasize the fact that the pointer variable will be used in a manner equivalent to an array.

Now we're ready to discuss pointer arithmetic. You can add and subtract integer values to/from pointers. If myArray is declared to be some type of array, the expression *(myArray+j) , where j is an integer, is equivalent to myArray[j] . For instance, in the above example where we had the expression secondArray[i].otherNumber , we could have written that as (*(secondArray+i)).otherNumber or more simply (secondArray+i)->otherNumber .

Note that for addition and subtraction of integers and pointers, the value of the pointer is not adjusted by the integer amount, but is adjusted by the amount multiplied by the size of the type to which the pointer refers in bytes. (For example, pointer + x can be thought of as pointer + (x * sizeof(*type)) .)

One pointer may also be subtracted from another, provided they point to elements of the same array (or the position just beyond the end of the array). If you have a pointer that points to an element of an array, the index of the element is the result when the array name is subtracted from the pointer. Here's an example.

You may be wondering how pointers and multidimensional arrays interact. Let's look at this a bit in detail. Suppose A is declared as a two dimensional array of floats ( float A[D1][D2]; ) and that pf is declared a pointer to a float. If pf is initialized to point to A[0][0], then *(pf+1) is equivalent to A[0][1] and *(pf+D2) is equivalent to A[1][0]. The elements of the array are stored in row-major order.

Let's look at a slightly different problem. We want to have a two dimensional array, but we don't need to have all the rows the same length. What we do is declare an array of pointers. The second line below declares A as an array of pointers. Each pointer points to a float. Here's some applicable code:

We also note here something curious about array indexing. Suppose myArray is an array and i is an integer value. The expression myArray[i] is equivalent to i[myArray] . The first is equivalent to *(myArray+i) , and the second is equivalent to *(i+myArray) . These turn out to be the same, since the addition is commutative.

Pointers can be used with pre-increment or post-decrement, which is sometimes done within a loop, as in the following example. The increment and decrement applies to the pointer, not to the object to which the pointer refers. In other words, *pArray++ is equivalent to *(pArray++) .

Pointers in Function Arguments [ edit | edit source ]

Often we need to invoke a function with an argument that is itself a pointer. In many instances, the variable is itself a parameter for the current function and may be a pointer to some type of structure. The ampersand ( & ) character is not needed in this circumstance to obtain a pointer value, as the variable is itself a pointer. In the example below, the variable pStruct , a pointer, is a parameter to function FunctTwo , and is passed as an argument to FunctOne .

The second parameter to FunctOne is an int. Since in function FunctTwo , mValue is a pointer to an int, the pointer must first be dereferenced using the * operator, hence the second argument in the call is *mValue . The third parameter to function FunctOne is a pointer to a long. Since pAA is itself a pointer to a long, no ampersand is needed when it is used as the third argument to the function.

Pointers and Text Strings [ edit | edit source ]

Historically, text strings in C have been implemented as arrays of characters, with the last byte in the string being a zero, or the null character '\0'. Most C implementations come with a standard library of functions for manipulating strings. Many of the more commonly used functions expect the strings to be null terminated strings of characters. To use these functions requires the inclusion of the standard C header file "string.h".

A statically declared, initialized string would look similar to the following:

The variable myFormat can be viewed as an array of 21 characters. There is an implied null character ('\0') tacked on to the end of the string after the 'd' as the 21st item in the array. You can also initialize the individual characters of the array as follows:

An initialized array of strings would typically be done as follows:

The initialization of an especially long string can be split across lines of source code as follows.

The library functions that are used with strings are discussed in a later chapter.

Pointers to Functions [ edit | edit source ]

C also allows you to create pointers to functions. Pointers to functions syntax can get rather messy. As an example of this, consider the following functions:

Declaring a typedef to a function pointer generally clarifies the code. Here's an example that uses a function pointer, and a void * pointer to implement what's known as a callback. The DoSomethingNice function invokes a caller supplied function TalkJive with caller data. Note that DoSomethingNice really doesn't know anything about what dataPointer refers to.

Some versions of C may not require an ampersand preceding the TalkJive argument in the DoSomethingNice call. Some implementations may require specifically casting the argument to the MyFunctionType type, even though the function signature exacly matches that of the typedef.

Function pointers can be useful for implementing a form of polymorphism in C. First one declares a structure having as elements function pointers for the various operations to that can be specified polymorphically. A second base object structure containing a pointer to the previous structure is also declared. A class is defined by extending the second structure with the data specific for the class, and static variable of the type of the first structure, containing the addresses of the functions that are associated with the class. This type of polymorphism is used in the standard library when file I/O functions are called.

A similar mechanism can also be used for implementing a state machine in C. A structure is defined which contains function pointers for handling events that may occur within state, and for functions to be invoked upon entry to and exit from the state. An instance of this structure corresponds to a state. Each state is initialized with pointers to functions appropriate for the state. The current state of the state machine is in effect a pointer to one of these states. Changing the value of the current state pointer effectively changes the current state. When some event occurs, the appropriate function is called through a function pointer in the current state.

Practical use of function pointers in C [ edit | edit source ]

Function pointers are mainly used to reduce the complexity of switch statement. Example with switch statement:

Without using a switch statement:

Function pointers may be used to create a struct member function:

Use to implement this pointer (following code must be placed in library).

Examples of pointer constructs [ edit | edit source ]

Below are some example constructs which may aid in creating your pointer.

sizeof [ edit | edit source ]

The sizeof operator is often used to refer to the size of a static array declared earlier in the same function.

To find the end of an array (example from wikipedia:Buffer overflow ):

To iterate over every element of an array, use

Note that the sizeof operator only works on things defined earlier in the same function. The compiler replaces it with some fixed constant number. In this case, the buffer was declared as an array of 10 char's earlier in the same function, and the compiler replaces sizeof(buffer) with the number 10 at compile time (equivalent to us hard-coding 10 into the code in place of sizeof(buffer) ). The information about the length of buffer is not actually stored anywhere in memory (unless we keep track of it separately) and cannot be programmatically obtained at run time from the array/pointer itself.

Often a function needs to know the size of an array it was given -- an array defined in some other function. For example,

Unfortunately, (in C and C++) the length of the array cannot be obtained from an array passed in at run time, because (as mentioned above) the size of an array is not stored anywhere. The compiler always replaces sizeof with a constant. This sum() routine needs to handle more than just one constant length of an array.

There are some common ways to work around this fact:

  • Write the function to require, for each array parameter, a "length" parameter (which has type "size_t"). (Typically we use sizeof at the point where this function is called).
  • Use of a convention, such as a null-terminated string to mark the end of the array.
  • Instead of passing raw arrays, pass a structure that includes the length of the array (such as ".length") as well as the array (or a pointer to the first element); similar to the string or vector classes in C++.

It's worth mentioning that sizeof operator has two variations: sizeof ( type ) (for instance: sizeof (int) or sizeof (struct some_structure) ) and sizeof expression (for instance: sizeof some_variable.some_field or sizeof 1 ).

External Links [ edit | edit source ]

  • "Common Pointer Pitfalls" by Dave Marshall

assignment to array c

  • Book:C Programming

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C Functions

C structures.

Arrays are used to store multiple values in a single variable, instead of declaring separate variables for each value.

To create an array, define the data type (like int ) and specify the name of the array followed by square brackets [] .

To insert values to it, use a comma-separated list, inside curly braces:

We have now created a variable that holds an array of four integers.

Access the Elements of an Array

To access an array element, refer to its index number .

Array indexes start with 0 : [0] is the first element. [1] is the second element, etc.

This statement accesses the value of the first element [0] in myNumbers :

Change an Array Element

To change the value of a specific element, refer to the index number:

Loop Through an Array

You can loop through the array elements with the for loop.

The following example outputs all elements in the myNumbers array:

Set Array Size

Another common way to create arrays, is to specify the size of the array, and add elements later:

Using this method, you should know the number of array elements in advance, in order for the program to store enough memory.

You are not able to change the size of the array after creation.

C Exercises

Test yourself with exercises.

Create an array of type int called myNumbers .

Start the Exercise

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Pointer to an Array in C

It is most likely that you would not understand this section until you are through with the chapter 'Pointers'.

Assuming you have some understanding of pointers in C, let us start: An array name is a constant pointer to the first element of the array. Therefore, in the declaration −

balance is a pointer to &balance[0], which is the address of the first element of the array balance. Thus, the following program fragment assigns p as the address of the first element of balance −

It is legal to use array names as constant pointers, and vice versa. Therefore, *(balance + 4) is a legitimate way of accessing the data at balance[4].

Once you store the address of the first element in 'p', you can access the array elements using *p, *(p+1), *(p+2) and so on. Given below is the example to show all the concepts discussed above −

When the above code is compiled and executed, it produces the following result −

In the above example, p is a pointer to double, which means it can store the address of a variable of double type. Once we have the address in p, *p will give us the value available at the address stored in p, as we have shown in the above example.

Integer Array in C – How to Declare Int Arrays with C Programming

Dionysia Lemonaki

In this article, you will learn how to work with arrays in C.

I will first explain how to declare and initialize arrays.

Then, I will also go over how to access and change items in an array in C with the help of code examples along the way.

Let's get into it!

What Is An Array in C Programming?

An array is a data structure that stores multiple values in a single variable and in a sequential order that is easily accessible.

Arrays in C are a collection of values that store items of the same data type – an integer array holds only elements of the type int , a float array holds only elements of the type float , and so on.

How to Declare an Integer Array in C Programming

The general syntax for declaring an array in C looks as you can see it in the code snippet below:

Let's take the following example:

Let's break it down:

  • I first defined the data type of the array, int .
  • I then specified the name, my_numbers , followed by a pair of opening and closing square brackets, [] .
  • Inside the square brackets, I defined the size ( 5 ), meaning the array can hold 5 integer values.
  • Finally, I ended the statement with a semicolon ( ; ).

Once you have set the array type and size during declaration, the array can't hold items of another type.

The array is also fixed in size, meaning you cannot add or remove items.

How to Initialize an Integer Array in C Programming

There are a couple of ways you can initialize an integer array in C.

The first way is to initialize the array during declaration and insert the values inside a pair of opening and closing curly braces, {} .

The general syntax to do that looks like this:

Let's take the array I declared in the previous section that can hold five integers and initialize it with some values:

In the example above, I placed five comma-separated values inside curly braces, and assigned those values to my_numbers through the assignment operator ( = ).

Something to note here is that when you specify the size of the array, you can assign less number of elements, like so:

Although the size of the array is 5 , I only placed three values inside it.

The array can hold two more items, and those remaining two positions have a default value of 0 .

Another way to initialize an array is to not specify the size, like so:

Even though I did not set the size of the array, the compiler knows its size because it knows the number of items stored inside it.

How to Access Items in an Integer Array in C Programming

To access an element in an array, you have to specify the index of the element in square brackets after the array name.

The syntax to access an element looks like this:

In C and programming in general, an array index always starts at 0 , becuase in computer science, counting starts from 0 .

So, the first item in an array has an index of 0 , the second item has an index of 1 , the third item has an index of 2 , and so on.

Taking the same array from the previous section, here is how you would access the first element, that is, 10 :

Keep in mind that the last element in an array has an index of array_size -1 – it is always one less than the size of the array. So, in an array that holds five elements, the index of the last element is 4 .

If in an array of five items, you try to access the last element by using an index of 5 , the program will run, but the element is not available, and you will get undefined behavior:

How to Change Items in an Integer Array in C Programming

To change the value of a specific element, specify its index number and, with the assignment operator, = , assign a new value:

In the example above, I changed the first item in the array from 10 to 11 .

And there you have it! You now know the basics of working with arrays in C.

To learn more about C, give this C beginner's handbook a read to become familiar with the basics of the language.

Thanks for reading, and happy coding!

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In C programming, you can create an array of arrays. These arrays are known as multidimensional arrays. For example,

Here, x is a two-dimensional (2d) array. The array can hold 12 elements. You can think the array as a table with 3 rows and each row has 4 columns.

Two dimensional array in C programming

Similarly, you can declare a three-dimensional (3d) array. For example,

Here, the array y can hold 24 elements.

  • Initializing a multidimensional array

Here is how you can initialize two-dimensional and three-dimensional arrays:

Initialization of a 2d array

Initialization of a 3d array.

You can initialize a three-dimensional array in a similar way to a two-dimensional array. Here's an example,

Example 1: Two-dimensional array to store and print values

Example 2: sum of two matrices, example 3: three-dimensional array, table of contents.

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In C++, an array is a data structure that is used to store multiple values of similar data types in a contiguous memory location.

For example , if we have to store the marks of 4 or 5 students then we can easily store them by creating 5 different variables but what if we want to store marks of 100 students or say 500 students then it becomes very challenging to create that numbers of variable and manage them. Now, arrays come into the picture that can do it easily by just creating an array of the required size.

Arrays-in-C++

Properties of Arrays in C++

  • An Array is a collection of data of the same data type, stored at a contiguous memory location.
  • Indexing of an array starts from 0. It means the first element is stored at the 0th index, the second at 1st, and so on.
  • Elements of an array can be accessed using their indices.
  • Once an array is declared its size remains constant throughout the program.
  • An array can have multiple dimensions.
  • The number of elements in an array can be determined using the sizeof operator.
  • We can find the size of the type of elements stored in an array by subtracting adjacent addresses.

Array Declaration in C++

In C++, we can declare an array by simply specifying the data type first and then the name of an array with its size.

  • int: It is the type of data to be stored in the array. We can also use other data types such as char, float, and double.
  • arr: It is the name of the array.
  • 5: It is the size of the array which means only 5 elements can be stored in the array.

array declaration in c++

Initialization of Array in C++

In C++, we can initialize an array in many ways but we will discuss some most common ways to initialize an array. We can initialize an array at the time of declaration or after declaration.

1. Initialize Array with Values in C++

We have initialized the array with values. The values enclosed in curly braces ‘{}’ are assigned to the array. Here, 1 is stored in arr[0], 2 in arr[1], and so on. Here the size of the array is 5.

2. Initialize Array with Values and without Size in C++

We have initialized the array with values but we have not declared the length of the array, therefore, the length of an array is equal to the number of elements inside curly braces.

3. Initialize Array after Declaration (Using Loops)

We have initialized the array using a loop after declaring the array. This method is generally used when we want to take input from the user or we cant to assign elements one by one to each index of the array. We can modify the loop conditions or change the initialization values according to requirements.

4. Initialize an array partially in C++

Here, we have declared an array ‘partialArray’ with size ‘5’ and with values ‘1’ and ‘2’ only. So, these values are stored at the first two indices, and at the rest of the indices ‘0’ is stored.

5. Initialize the array with zero in C++

We can initialize the array with all elements as ‘0’ by specifying ‘0’ inside the curly braces. This will happen in case of zero only if we try to initialize the array with a different value say ‘2’ using this method then ‘2’ is stored at the 0th index only.

Accessing an Element of an Array in C++

Elements of an array can be accessed by specifying the name of the array, then the index of the element enclosed in the array subscript operator []. For example, arr[i].

Example 1: The C++ Program to Illustrate How to Access Array Elements

Update array element.

To update an element in an array, we can use the index which we want to update enclosed within the array subscript operator and assign the new value.

Traverse an Array in C++

We can traverse over the array with the help of a loop using indexing in C++. First, we have initialized an array ‘table_of_two’ with a multiple of 2. After that, we run a for loop from 0 to 9 because in an array indexing starts from zero. Therefore, using the indices we print all values stored in an array.

Example 2: The C++ Program to Illustrate How to Traverse an Array

Size of an array in c++.

In C++, we do not have the length function as in Java to find array size but we can calculate the size of an array using sizeof() operator trick. First, we find the size occupied by the whole array in the memory and then divide it by the size of the type of element stored in the array. This will give us the number of elements stored in the array.

Example 3: The C++ Program to Illustrate How to Find the Size of an Array

Relation between arrays and pointers in c++.

In C++, arrays and pointers are closely related to each other. The array name is treated as a pointer that stored the memory address of the first element of the array. As we have discussed earlier, In array elements are stored at contiguous memory locations that’s why we can access all the elements of an array using the array name.

Example 4: Illustrating the Relationship between Array and Pointers

Explanation:

In the above code, we first define an array “ arr ” and then declare a pointer “ ptr ” and assign the array “arr” to it. We are able to assign arr to ptr because arr is also a pointer. After that, we print the memory address of arr using reference operator ( & ) and also print the address stored in pointer ptr and we can see arr and ptr, both stores the same memory address.

Example 5: Printing Array Elements without Indexing in C++

We generally access and print the array elements using indexing. For example to access the first element we use array_name[0]. We have discussed above that the array name is a pointer that stored the address of the first element and array elements are stored at contiguous locations. Now, we are going to access the elements of an array using the array name only.

Explanation

In the above code, we first declared an array “ arr ” with four elements. After that, we are printing the array elements. Let’s discuss how we do it. We discussed that the array name is a pointer that stores the address of the first element of an array so, to print the first element we have dereferenced that pointer (*arr) using dereferencing operator (*) which prints the data stored at that address.

To print the second element of an array we first add 1 to arr which is equivalent to (address of arr + size_of_one_element *1) that takes the pointer to the address just after the first one and after that, we dereference that pointer to print the second element. Similarly, we print rest of the elements of an array without using indexing.

Passing Array to Function in C++

To use arrays efficiently we should know how to pass arrays to function. We can pass arrays to functions as an argument same as we pass variables to functions but we know that the array name is treated as a pointer using this concept we can pass the array to functions as an argument and then access all elements of that array using pointer.

So ultimately, arrays are always passed as pointers to the function. Let’s see 3 ways to pass an array to a function that are majorly used.

1. Passing Array as a Pointer

In this method, we simply pass the array name in function call which means we pass the address to the first element of the array. In this method, we can modify the array elements within the function.

2. Passing Array as an Unsized Array

In this method, the function accepts the array using a simple array declaration with no size as an argument.

3. Passing Array as a Sized Array

In this method, the function accepts the array using a simple array declaration with size as an argument. We use this method by sizing an array just to indicate the size of an array.

Note: Array will be treated as a pointer in the passed function no matter what method we use. As the array are passed as pointers, they will loose the information about its size leading to a phenomenon named as Array Decay.

Example: Illustrating Different Ways to Pass Arrays to a Function

  • Multidimensional Arrays in C++

Arrays declared with more than one dimension are called multidimensional arrays. The most widely used multidimensional arrays are 2D arrays and 3D arrays. These arrays are generally represented in the form of rows and columns.

Multidimensional Array Declaration

  • Data_Type:  Type of data to be stored in the array.
  • Array_Name:  Name of the array.
  • Size1, Size2,…, SizeN:  Size of each dimension.

Two Dimensional Array in C++

In C++, a two-dimensional array is a grouping of elements arranged in rows and columns. Each element is accessed using two indices: one for the row and one for the column, which makes it easy to visualize as a table or grid.

Syntax of 2D array

  • n: Number of rows.

two dimensional array in c++

Example: The C++ Program to Illustrate the Two-Dimensional Array

In the above code we have declared a 2D array with 4 rows and 4 columns after that we initialized the array with the value of (i+j) in every iteration of the loop. Then we are printing the 2D array using a nested loop and we can see in the below output that there are 4 rows and 4 columns.

Three-Dimensional Array in C++

The 3D array uses three dimensions. A collection of various two-dimensional arrays piled on top of one another can be used to represent it. Three indices—the row index, column index, and depth index are used to uniquely identify each element in a 3D array.

Declaration of Three-Dimensional Array in C++

To declare a 3D array in C++, we need to specify its third dimension along with 2D dimensions.

  • Data_Type:  Type of data to be stored in each element.
  • Array_Name:  Name of the array
  • D:  Number of 2D arrays or Depth of array.
  • R:  Number of rows in each 2D array.
  • C:  Number of columns in each 2D array.

three dimensional array in  c++

Example: The C++ Program to Illustrate the 3d Array

In the above code, we have declared a 3D array and then initialized it using three nested for loops. After that, we printed all layers of the 3D array again using three nested for loops as seen in the output.

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cppreference.com

Array declaration.

Declares an object of array type.

[ edit ] Syntax

An array declaration is any simple declaration whose declarator has the form

A declaration of the form T a [ N ] ; , declares a as an array object that consists of N contiguously allocated objects of type T . The elements of an array are numbered ​ 0 ​ , …, N - 1 , and may be accessed with the subscript operator [] , as in a [ 0 ] , …, a [ N - 1 ] .

Arrays can be constructed from any fundamental type (except void ), pointers , pointers to members , classes , enumerations , or from other arrays of known bound (in which case the array is said to be multi-dimensional). In other words, only object types except for array types of unknown bound can be element types of array types. Array types of incomplete element type are also incomplete types.

There are no arrays of references or arrays of functions.

Applying cv-qualifiers to an array type (through typedef or template type manipulation) applies the qualifiers to the element type, but any array type whose elements are of cv-qualified type is considered to have the same cv-qualification.

When used with new[]-expression , the size of an array may be zero; such an array has no elements:

[ edit ] Assignment

Objects of array type cannot be modified as a whole: even though they are lvalues (e.g. an address of array can be taken), they cannot appear on the left hand side of an assignment operator:

[ edit ] Array-to-pointer decay

There is an implicit conversion from lvalues and rvalues of array type to rvalues of pointer type: it constructs a pointer to the first element of an array. This conversion is used whenever arrays appear in context where arrays are not expected, but pointers are:

[ edit ] Multidimensional arrays

When the element type of an array is another array, it is said that the array is multidimensional:

Note that when array-to-pointer decay is applied, a multidimensional array is converted to a pointer to its first element (e.g., a pointer to its first row or to its first plane): array-to-pointer decay is applied only once.

[ edit ] Arrays of unknown bound

If expr is omitted in the declaration of an array, the type declared is "array of unknown bound of T", which is a kind of incomplete type , except when used in a declaration with an aggregate initializer :

Because array elements cannot be arrays of unknown bound, multidimensional arrays cannot have unknown bound in a dimension other than the first:

If there is a preceding declaration of the entity in the same scope in which the bound was specified, an omitted array bound is taken to be the same as in that earlier declaration, and similarly for the definition of a static data member of a class:

References and pointers to arrays of unknown bound can be formed, but cannot (until C++20) and can (since C++20) be initialized or assigned from arrays and pointers to arrays of known bound. Note that in the C programming language, pointers to arrays of unknown bound are compatible with pointers to arrays of known bound and are thus convertible and assignable in both directions.

Pointers to arrays of unknown bound cannot participate in pointer arithmetic and cannot be used on the left of the subscript operator , but can be dereferenced.

[ edit ] Array rvalues

Although arrays cannot be returned from functions by value and cannot be targets of most cast expressions, array prvalues may be formed by using a type alias to construct an array temporary using brace-initialized functional cast .

Array xvalues may be formed directly by accessing an array member of a class rvalue or by using std::move or another cast or function call that returns an rvalue reference.

[ edit ] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[ edit ] See also

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COMMENTS

  1. C array declaration and assignment?

    Why does C++ support memberwise assignment of arrays within structs, but not generally? Arrays are not pointers. x here does refer to an array, though in many circumstances this "decays" (is implicitly converted) to a pointer to its first element. Likewise, y too is the name of an array, not a pointer. You can do array assignment within structs:

  2. Assign multiple values to array in C

    The int_array_init method will safely assign junk if the number of arguments is fewer than the node_ct. The junk assignment ought to be easier to catch and debug. The junk assignment ought to be easier to catch and debug.

  3. C Arrays

    Array in C is one of the most used data structures in C programming. It is a simple and fast way of storing multiple values under a single name. In this article, we will study the different aspects of array in C language such as array declaration, definition, initialization, types of arrays, array syntax, advantages and disadvantages, and many more.

  4. C Arrays (With Examples)

    Arrays in C. An array is a variable that can store multiple values. For example, if you want to store 100 integers, you can create an array for it. int data[100]; How to declare an array? dataType arrayName[arraySize]; For example, float mark[5]; Here, we declared an array, mark, of floating-point type. And its size is 5.

  5. Arrays in C

    Same as in one-dimensional array, we can assign values to the elements of a 2-dimensional array in 2 ways as well. In the first method, just assign a value to the elements of the array. If no value is assigned to any element, then its value is assumed to be zero. Suppose we declared a 2-dimensional array a[2][2]. Now, we need to assign values ...

  6. Array declaration

    Arrays of constant known size can use array initializers to provide their initial values: int a [5]={1, 2, 3};// declares int [5] initialized to 1,2,3,0,0char str []="abc";// declares char [4] initialized to 'a','b','c','\0'. In function parameter lists, additional syntax elements are allowed within the array declarators: the keyword static and ...

  7. Arrays in C programming with examples

    Example of Array In C programming to find out the average of 4 integers. #include <stdio.h> int main() { int avg = 0; int sum =0; int x=0; /* Array- declaration - length 4*/ int num[4]; /* We are using a for loop to traverse through the array. * while storing the entered values in the array.

  8. Arrays in C

    Arrays in C are a kind of data structure that can store a fixed-size sequential collection of elements of the same type. Arrays are used to store a collection of data, but it is often more useful to think of an array as a collection of variables of the same type. An array in C is a collection of data items of similar data type.

  9. C Programming/Pointers and arrays

    C Programming/Pointers and arrays. Pointer a pointing to variable b. Note that b stores a number, whereas a stores the address of b in memory (1462) A pointer is a value that designates the address (i.e., the location in memory), of some value. Pointers are variables that hold a memory location. There are four fundamental things you need to ...

  10. C Arrays

    Arrays are used to store multiple values in a single variable, instead of declaring separate variables for each value. To create an array, define the data type (like int) and specify the name of the array followed by square brackets [] . To insert values to it, use a comma-separated list, inside curly braces: We have now created a variable that ...

  11. Pointer to an Array in C

    Assuming you have some understanding of pointers in C, let us start: An array name is a constant pointer to the first element of the array. Therefore, in the declaration −. balance is a pointer to &balance [0], which is the address of the first element of the array balance. Thus, the following program fragment assigns p as the address of the ...

  12. Integer Array in C

    The general syntax for declaring an array in C looks as you can see it in the code snippet below: data_type array_name[array_size]; Let's take the following example: int my_numbers[5]; Let's break it down: I first defined the data type of the array, int. I then specified the name, my_numbers, followed by a pair of opening and closing square ...

  13. Initialize an Array in C

    Initialize an Array in C. Published on August 3, 2022. C Programming; By Vijaykrishna Ram. While we believe that this content benefits our community, we have not yet thoroughly reviewed it. If you have any suggestions for improvements, please let us know by clicking the "report an issue" button at the bottom of the tutorial.

  14. Dynamic Array in C

    A Dynamic Array is allocated memory at runtime and its size can be changed later in the program. We can create a dynamic array in C by using the following methods: Using malloc () Function. Using calloc () Function. Resizing Array Using realloc () Function. Using Variable Length Arrays (VLAs) Using Flexible Array Members.

  15. Array of Strings in C

    But an array of strings in C is a two-dimensional array of character types. Each String is terminated with a null character (\0). It is an application of a 2d array. Syntax: char variable_name[r] = {list of string}; Here, var_name is the name of the variable in C. r is the maximum number of string values that can be stored in a string array.

  16. C/C++ arrays assignment

    You can assign it in the same way: a = {1, 2, 3}. But that's actually C++0x ("extended initializer lists"). If you need to reassign the array in each loop iteration, you can still use memcpy. @archer: then you're almost surely wrong. Array allocation on the stack in just a stack pointer addition/subtraction.

  17. C Multidimensional Arrays (2d and 3d Array)

    C Multidimensional Arrays. In C programming, you can create an array of arrays. These arrays are known as multidimensional arrays. For example, float x[3][4]; Here, x is a two-dimensional (2d) array. The array can hold 12 elements. You can think the array as a table with 3 rows and each row has 4 columns.

  18. c++

    "Array names are constant not l-value" Names which refer to arrays are lvalues, as all id-expressions which refer to functions, variables or data members are lvalues [expr.prim.general]/8. It's a bit tricky: the assignment operator requires a modifiable lvalue, but what that is, is not defined in the C++ Standard, only in the C Standard: 6.3.2.1/1 "A modifiable lvalue is an lvalue that does ...

  19. C++ Arrays

    In C++, we can declare an array by simply specifying the data type first and then the name of an array with its size. data_type array_name[Size_of_array]; Example. int arr[5]; Here, int: It is the type of data to be stored in the array. We can also use other data types such as char, float, and double.

  20. Array declaration

    References and pointers to arrays of unknown bound can be formed, but cannot (until C++20) and can (since C++20) be initialized or assigned from arrays and pointers to arrays of known bound. Note that in the C programming language, pointers to arrays of unknown bound are compatible with pointers to arrays of known bound and are thus convertible and assignable in both directions.

  21. Getting C error "assignment to expression with array type"

    It modifies the length of the value stored. With %f you are attempting to store a 32-bit floating point number in a 64-bit variable. Since the sign-bit, biased exponent and mantissa are encoded in different bits depending on the size, using %f to attempt to store a double always fails` (e.g. the sign-bit is still the MSB for both, but e.g. a float has an 8-bit exponent, while a double has 11 ...