The calloc function is a memory allocation function in the C standard library that is used to allocate memory for an array of nitems elements, each of which has a size of size bytes. The syntax of the calloc function is as follows:

void *calloc(size_t nitems, size_t size);

The nitems argument is the number of elements to be allocated, and size is the size of each element. The function returns a pointer to the allocated memory block if the allocation is successful, and NULL if the allocation fails.

The calloc function initializes all the bytes in the allocated memory block to zero. This is different from the malloc function, which does not initialize the allocated memory block.

Here is an example that demonstrates how to use the calloc function to allocate memory for an array:

#include <stdio.h>
#include <stdlib.h>

int main(void) {
    int n = 10;
    int *array = (int *)calloc(n, sizeof(int));

    if (array == NULL) {
        printf("Memory allocation failed\n");
        return 1;
    }

    for (int i = 0; i < n; i++) {
        printf("%d ", array[i]);
    }
    printf("\n");

    free(array);
    return 0;
}

In this example, the calloc function is used to allocate memory for an array of 10 int elements. The size of each element is sizeof(int). The program then uses a for loop to print out the elements of the array. Since the calloc function initializes all the bytes in the allocated memory block to zero, the output of the program is:

0 0 0 0 0 0 0 0 0 0

Note that the calloc function returns NULL if the allocation fails. It is a good practice to check the value returned by the calloc function to make sure that the allocation was successful before using the allocated memory block. Also, just like with the malloc function, you must call the free function to release the allocated memory block when you are done using it.