Confused about getchar() function

That's because getchar() is a blocking function.

You should read about blocking functions, which basically make the process wait for something to happen.

The implementation of this waiting behavior depends on the function, but usually it's a loop that waits for some event to happen.

For the case of the getchar() function, this probably is implemented as a loop that constantly reads a file (stdin for this case) and checks weather the file is modified. If the file is modified, the loop behaves by doing something else.

The getchar() function will simply wait until it receives a character, holding the program up until it does.

A character is sent when you hit the enter key; under a Windows OS, it will send a carriage return (CR) and a line-feed (LF).

See this CodingHorror post for a nicely put explanation.

(...the explanation of the CR+LF part, not the getchar() blocking part)