#include<stdio.h>
#include<assert.h>

const char* mystrstr(const char* str1, const char* str2) {
	assert(str1 != NULL);
	assert(str2 != NULL);
	assert(*str1 != '\0');
	assert(*str2 != '\0');
	const char* black = str1;
	while (*black != '\0') {
		const char* red = black;
		const char* sub = str2;
		while (*red != '\0' && *sub != '\0'&& *red == *sub) {
			red++;
			sub++;
		}
		if (*red == '\0') {
			black++;
		}else if (*sub == '\0') {
			return black;
		}else {
			black++;
		}
	}
}
int main() {
	char str1[] = "hello";
	char str2[] = "ello";
	char* str = strstr(str1, str2);
	printf("%s\n", str);
	return 0;
}