find()函数

#include <iostream>
#include <cstring>
using namespace std;
int main(){
    string a, b, c, d;
    cin >> a >> b >> c;
    d = a + b;
    if((int)(d.find(c)) != -1){
        cout << c << " is substring of " << a << " and " << b;
    }else{
        cout << c << " is not substring of " << a << " and " << b;
    }
    return 0;
}