explain answers please

Assuming C++, what kinds of errors are these (lexical, syntax, semantic)? int = 3; int = ?3; int y = 3; x = y; "Hello, World! int x; double y = 2.5; x = y; void sum(int, int); sum(1, 2, 3); my int++ z = y/x;//y is 1, x is 0