程序代码：

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

string p(string s1,string &s2){
    for(size_t i=0;i!=s1.size();++i){
        switch (s1[i]){
            case 'a':
            case 'A':
        s2.push_back(s1[i]);
        ++i;
        break;
        case 'o':
        case 'O':
        s2.push_back(s1[i]);
        ++i;
        break;
        case 'e':
        case 'E':
        s2.push_back(s1[i]);
        ++i;
        break;
        case 'i':
        case 'I':
        s2.push_back(s1[i]);
        ++i;
        break;
        case 'u':
        case 'U':
        s2.push_back(s1[i]);
        ++i;
        break;
        }
        
        }
        return s2;}
int main(){
    string s1,s2;
    cin>>s1;
    p(s1,s2);
cout<<s2<<endl;
return 0;

} 

程序代码：

string p(string s1,string &s2){
    size_t len,i=0;
    len=s1.size();
    for(;i<len;++i){
        switch (s1[i]){
            case 'a':
            case 'A':       
            case 'o':
            case 'O':
            case 'e':
            case 'E':
            case 'i':
            case 'I':
            case 'u':
            case 'U':
                s2.push_back(s1[i]);
                break;
        }
        
        }
        return s2;}