怎么把控制台程序转换为窗体程序？？

#include "stdafx.h"
#include <iostream>
#include <string>
using namespace std;
bool isAlpha(char c) {
    if (c >= 'a' && c <= 'z') return true;
    if (c >= 'A' && c <= 'Z') return true;
    return false;
}
 
int main() {
    string s; getline(cin, s);
    for (int i = 0; i < s.length(); ++i) {
        if (isAlpha(s[i])) {
            if (s[i] == 'a') s[i] = 'z';
            else if (s[i] == 'A') s[i] = 'Z';
            else s[i] = s[i] - 1;
        }
    }
    cout << s << endl;
    system("pause");
    return 0;
}

转换为窗体全是错误