PAT Advanced 1050 String Subtraction (20 分)

Given two strings S​1​​ and S​2​​, S=S​1​​−S​2​​ is defined to be the remaining string after taking all the characters in S​2​​ from S​1​​. Your task is simply to calculate S​1​​−S​2​​ for any given strings. However, it might not be that simple to do it fast.

Input Specification:

Each input file contains one test case. Each case consists of two lines which gives S​1​​ and S​2​​, respectively. The string lengths of both strings are no more than 1. It is guaranteed that all the characters are visible ASCII codes and white space, and a new line character signals the end of a string.

Output Specification:

For each test case, print S​1​​−S​2​​ in one line.

Sample Input:

They are students.
aeiou

Sample Output:

Thy r stdnts.

#include <iostream>
using namespace std;

int main(){
    string s1,s2,res="";
    getline(cin,s1);
    getline(cin,s2);
    for(int i=0;i<s1.length();i++){
        if(s2.find(s1[i])==s2.npos) res+=s1[i];
    }
    cout<<res;
    system("pause");
    return 0;
}