1.在下标为n处插入y

#include <iostream>
#include <algorithm>
#include <string>
using namespace std;

string x,y;
int n;

int main()
{
	cin>>x>>y>>n;
	x.insert(n,y); //在下表为n处插入y
	cout<<x<<endl;

	return 0;
}

2…待续