What is the difference between single quoted and double quoted declaration of char array?

In C, when a character array is initialized with a double-quoted string and the array size is not specified, the compiler automatically allocates one extra space for string terminator ‘\0’.

Example

The below example demonstrates the initialization of a char array with a double-quoted string without specifying the size. The below program prints 6 as output.

C

// C program to demonstrate the initialization of a char
// array with a double quoted string without specifying the
// size.

#include <stdio.h>
int main()
{
    // size of arr[] is 6 as it is '\0' terminated
    char arr[] = "geeks";

    printf("%lu", sizeof(arr));

    return 0;
}

Output

6

On the other hand, when the character array is initialized with comma comma-separated list of characters and the array size is not specified, the compiler doesn’t create extra space for the string terminator ‘\0’.

Example

The below example demonstrates the initialization of a char array with comma separated list of characters without specifying the size of the array.

C

// C program to demonstrates the initialization of a char
// array with comma separated list of characters without
// specifying size of array.

#include <stdio.h>
int main()
{
    // arr[] is not terminated with '\0'
    // and its size is 5
    char arr[] = { 'g', 'e', 'e', 'k', 's' };

    printf("%lu", sizeof(arr));

    return 0;
}

Output

5

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