Point out the error (if any) in the following C code?

#include <stdlib.h>
#include <stdio.h>
int main(void)
{
    int* p = NULL;
    struct S *s = NULL;
    void(*f)(int, double) = NULL;
    char *ptr = malloc(15);
    if (ptr == NULL) printf("Out of memory");
    free(ptr);
}

A. strlen() B. strlength() C. stringlen() D. strsize()

A. To print formatted text to the standard output B. To read text from the standard input C. To open a file D. To close a file

A. math.h B. stdlib.h C. cmath.h D. algorithm.h

A. Compares two strings and returns an integer indicating their relationship B. Copies one string to another C. Concatenates two strings D. Searches for a substring