# include <stdio.h>

int find_substr(char* s1, char* s2);

void main()
{
	if(find_substr("C is fun", "is") != -1)
		printf("Substring is found.\n");
}

/* 定義子函數 */
int find_substr(char* s1, char* s2)
{
	register int t;
	char *p, *p2;

	for(t=0; s1[t]; t++)
	{
		p = &s1[t];
		p2 = s2;

		while(*p2 && *p2==*p)
		{
			p++;
			p2++;
		}
		if(! *p2)
			return t;
	}
	return -1;
}