Implementing Trial Scheme.[help]

[Trial]
Value=1

string str = parse.get <std::string>("Trial.Value");
    int i;
    stringstream(str) >> i;
    
    if(i >= 51){
         exit(1);
         }else{
 
 
    int a = i + 1;    // problem here is it can only work once, after that it will                  
                      //stop adding. so im stuck with Value=2
    
    stringstream ss;
    ss << a;
    
    ofstream file("config.ini");
    file << "[Trial]";
    file << "\nValue=";
    file << (ss, ios::ate); //problem here (i think)..no matter what value i put
                            // in sample.ini for example Value=25 ...the output 
                            //will still be Value=2

    file.close();