What is the difference between 100 and 101 in C language?
exit(0) indicates successful program termination & it is fully portable, While
exit(1) (usually) indicates unsucessful termination. However, it's usage is non-portable.
请注意，C标准定义了EXIT_SUCCESS和EXIT_FAILURE，以从C程序返回终止状态.
0和EXIT_SUCCESS是标准规定的表示终止成功的值，但是只有EXIT_FAILURE是返回不成功终止的标准值.不过，在许多实现中，1用于相同的用途.
参考:
C99 Standard: 7.20.4.3 The exit function
Para 5
最后，控制权返回到主机环境.如果status的值为零或