any.c

#include <stdio.h>

// return the index of the first occurrence of any character in matching occuring in string. -1 if none.
int any(char string[], char matching[]) {
    for (int i = 0; string[i] != '\0'; i++) {
        for (int j = 0; matching[j] != '\0'; j++) {
            if (string[i] == matching[j]) {
                return i;
            }
        }
    }

    return -1;
}

int main() {
    printf("%d\n", any("this is a test yo", "y"));
}