Find if a string s2 is a substring of string s1

Let s1 be the string in which we are looking for s2..
boolean Find(char *s1, char *s2) {
// Make a check to see if length of s2 is less than or equal to length of s1.. If not return false…
int i, j=0;
char flag = false;
int len = strlen(s2) - 1;
for(i=0;i{

if(flag = true && s2[j] != s1[i])
{
i--;
j=0;
flag = false;
}
else {

if(s2[j] == s1[i])
{
i++;
j++;
flag = true;
}
else
{
if(flag = false)
i++;
}
}
if(j == len)
{
return true;
}
}
return flag;
}