How to Perform Array Initialization in Computer Programming: C

After declaration of arrays, the process of initialization starts in computer programming. Array initialization in C may be perform in many ways will be discuss in this article. C programming provides to let the programmer initialize the array to specific values when it is declared, when it is required or etc. Each option have its own examples described in the article.

Initialization of all specified locations

Arrays can be initialized at the same time of declaration when their initial values are known in advance. Array elements can be initialized with data items of type int, char, float, etc.

int arr[5] = {15, 45, 85, 96, 69};

During compilation, 5 contiguous memory locations are reserved by the compiler for the array arr and all these locations are initialized as shown below:

If the size of an integer is 2 bytes, 10 bytes will be allocated for the array arr. Lets discuss another initialization

int arr[5] = {15, 58, 98, 89, 65, 54, 55, 25, 85};
This declaration will notify an error with a message Number of initial values are more than the size of the array arr

char str[7] = {'P', 'R', 'O', 'G', 'R', 'A', 'M'};

During compilation, 7 contiguous memory locations are reserved by the compiler for the variable str and all these locations are initialized as shown below:

In fact in place of character, ASCII values are stores in the memory. Since a character occupies 1 byte, 8 bytes will be allocated for the variable str.

Partial Array Initialization

C language also provides partial array initialization. If the number of values to be initialized is less than the size of an array, then the elements are initialized in order from 0th location. The remaining locations will be initialized to zero automatically. For example, consider the partial initialization shown below:

int arr[5] = {56, 76, 98};

Even though compiler allocates 5 memory locations, using this declaration statement, the compiler initialized first three locations with 56, 76 and 98. The next set of memory location are automatically initialized to 0's by the compiler as shown below:

Initialization without Size

Consider the declaration along with initialization shown below:
char str[] = {'P', 'R', 'O', 'G', 'R', 'A', 'M'};

In this declaration, even though we have not specified exact number of elements to be used in array str, the array size will be set to the total number of initial values specified. So, the array size will be set to 7 automatically. The array str is initialized as shown below:

String Initialization

Consider the declaration with string initialization:

char str[] = "PROGRAM";

The array str is initialized as shown below:

Even though the string "PROGRAM" contains 7 characters, because it is a string, it always ends with NULL character '\0'. So, the array size is 8 bytes i.e. string length + 1 byte for NULL character.

char str[8] = "PROGRAM"; is Correct, size of the array is string length + 1 byte for NULL character.
char str[7] = "PROGRAM";  is Wrong, size of the array should be minimum 8.

For string initialization, usually the programmer prefer the following declaration:
char str[] = "PROGRAM";

Reading and Writing Single Dimensional Array