why we use "<< " thes signs in cout function?

why we use "<" this sign double in cout function?

cout << thingie is symbolic for "send thingie to cout". cin >> thingie is symbolic for "send something to thingie from cin". The angle brackets denote the direction that data moves.

Whether >> and << are the best symbology for the behavior is up for debate, but it works reasonably well in practice.

int main()
{
    return 0;
}
commented: please give me another example because i knew this example. +0

a function with data type initiated will return a value , in this case , the main function which is

int main()
{
    return 0;
}

will return integer value , zero or true meaning your program execute without problems or errors, if non found after you compile your code.