4.1

#include <stdio.h>

int strrinde(char s[], char t[]){
	int i, j, k, pos = -1;
	for(i = 0; s[i] != '\0'; i++){
		for(j = i, k = 0; t[k] != '\0' && s[j] == t[k]; j++, k++)
			;
		if(k > 0 && t[k] == '\0')
			pos = i;
	}
	return pos;
}

main(){
	char s[] = "it's a test, yes, test!";
	char t[] = "test";

	int pos = strrinde(s, t);
	printf("%d\n", pos);
}