Even we write any other numer after return 0 still it prints correct output

Question

In explanation it is given that if we use any other number other than 0 program fails.

Answer 1

No, the return value is supposed to be used outside your program.

By returning 0 you give the signal to the outside that 'everything went okay', and by returning anything else you say: 'something went wrong'.

You should just accept and ignore it for now. Just go on with the tutorial. It will all become clearer when you learn about functions.