Find dangerous C functions in toy source

Challenge

Implement int count_dangerous_calls(const char *source) that returns the number of occurrences of any of the following identifiers as function calls in the source: strcpy, strcat, sprintf, gets, system. Match the identifier followed by ( (allowing whitespace) so substrings like mystrcpy( don't trigger.

Starter code

#include <stdio.h>
#include <string.h>
#include <ctype.h>

int count_dangerous_calls(const char *source) {
    /* TODO */
    return 0;
}