前二WA求助

#include <bits/stdc++.h>
using namespace std;

int main()
{
    int n;
    cin >> n;
    int a2,b2,a3,c;
    string s,s1,s3,s4,s_;
    cin >> s;
    for (int i=0;i<n;i++)
    {
    	cin >> c;
    	if (c==1)
    	{
    		cin >> s1;
    		s=s+s1;
    		cout << s <<endl;
    	}
    	if (c==2)
    	{
    		cin >> a2 >> b2;
    		s=s.substr(a2,b2);
    		cout << s <<endl;
    	}
    	if (c==3)
    	{
    		cin >> a3 >> s3;
    		s=s.substr(0,a3)+s3+s.substr(a3,s.length());
    		cout << s <<endl;
    	}
    	if (c==4)
    	{
    		cin >> s4;
    		cout << s.find(s4) <<endl;
    	}
    }
    return 0;
}