Why does cout produce the correct string output with <<, but not with +? [closed]

Answer 1

int x = 10;
cout << "Hello world!" << ++x;
return 0; 

If you want to increment a variable, you should use ++x. If you want to decrement it, use --x.

And, if you want to show a variable next to another one, or next to another string, use << between them.