C's main
function returns an int... that int goes to the program which executed it (the parent process, if you will) as an exit status code.
Specifically, on most operating systems, a 0 exit code signifies a normal run (no real errors), and non-zero means there was a problem and the program had to exit abnormally.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…