Why ! This is use after every statement.

Question

like to print hello world
cout << " Hello world! ";

Answer 1

To make a more dramatic phrase.

Answer 2

in programming, it is not valuable. it is just syntax in English to print a good message.

Answer 3

It is not at all compulsory to write '!' in ur cpp code. It is just the choice of coder or client. Most importantly it's part of English grammar not cpp.