#include <stdio.h>
#include <string.h> // for strcpy, strstr, strcat, strlen

int main() {
	char s[40];
	strcpy(s, "Ho! Ho! Ho! Happy Holidays!");
	char *t = strstr(s + 2*strlen("Ho"), "Ho");
	strcat(t, ":-)");
	printf("%s\n", t);
	return 0;
}

/** Output:
 * Ho! Ho! Happy Holidays!:-)
 **/