问题标题: 文件后缀修改器2.0

#include <io.h>
#include <iostream>
#include <cstring>
#include <string>
#include <windows.h>
using namespace std;
string s,c;
_finddata_t file;
long lf;
int pos=0;
string t;
int main(){
    cout<<"                 文件后缀修改器2.0             \n";
    cout<<"***********************************************\n";
    cout<<"*         输入start开始修改,exit退出          *\n";
    cout<<"***********************************************\n";
    cout<<"请选择:";
    cin>>t;
    if(t.compare("start")!=0) exit(0);
    cout<<"请先将文件存入文件夹中,并存入D盘!!!\n请输入要修改的扩展名(不带\".\"号):";
    cin>>s;
    s="."+s;
    cout<<"请输入要修改的文件夹名称:";
    getline(cin,c);
    getline(cin,c);
    string path="D:\\"+c+"\\";
    if((lf = _findfirst((path + "*.*").c_str(), &file))==string::npos){
        MessageBox(GetForegroundWindow(),"未查找到文件!!!","Error",MB_OK);
        exit(0);
    }else{
        system("color 0c");
        while(_findnext( lf, &file)==0){
            string str=file.name;
            for(int i=0;i<str.size();i++){
                if(str[i]=='.'){
                    pos=i;
                }
            }
            cout<<"修改:"<<str<<"为 ";
            Sleep(50);
            if(pos!=0) str.erase(pos,str.size()-pos);
            str.append(s);
            if(rename((path + string(file.name)).c_str(), (path + str).c_str()) == 0){
                cout<<str<<endl;
            }
        }
    }
    _findclose(lf);
    Sleep(500);
    system("color 0A");
    cout<<"修改完成!!!        \n";
    system("pause");
    cout<<"谢谢使用!!!";
    return 0;
}