how to export the computer time to text file without overwriting C++

1. record the computer time when user click on the mouse
2. export the time to a file ( .txt)
3. update the file

#include <time.h>
#include <stdio.h>
#include <iostream>
#include <fstream>
using namespace std;

int main()
{   //string record;

char key;

    ofstream fout;
    ifstream fin;

fin.open ("text.txt");
fout.open ("text1.txt");
    while(1){
        cin>>key;
             if (key=='a')
             {time_t currentTime = time(0);
               
               printf("The Current Time is %s", ctime(¤tTime));  
  
               fout << ctime(¤tTime);
                  
                 key=='0';

 
                       }
                       if (key =='b')
                       break;
                       }
                       fout.close();
system("PAUSE");
  return 0;
}