Why main function returns a integer ?

Answer 1

It doenst metter actually, you can make it void and don't have to return anything

Answer 2

because programs usually return with an integer code. 0 means regular exit, other means an error. depending the return value the caller can handle different outcomes.

Answer 3

By cpp standard prohibited use of void on main function, this mean cpp main return a int.
return 0 -> program normal end
return negative value -> abnormal finish, like -1