below you see a simple infinite loop.
I want to run the code inside the loop n seconds and after n seconds I will hit ctrl-z so that the loop terminates.
I dont want to type any other character to run the loop. It will loop infinite times until I enter ctrl-z

It depends on which system you are using. In Windows, they have something called called kbhit which will tell you when you hit a character. Unix is a bit more difficult. You may have to play with some ioctl things.