使用find函数就好了

openjudge

#include<bits/stdc++.h>
using namespace std;
int main(){
	string s1,s2;
	cin>>s1;
	cin>>s2;
	if(s1.find(s2)!=string::npos) cout<<s2<<" is substring of "<<s1;
	else if(s2.find(s1)!=string::npos) cout<<s1<<" is substring of "<<s2;
	else cout<<"No substring";
	return 0;
}
//题解勿抄，打一遍也好