左值lvalue 和 右值rvalue

1、lvalue: An expression that is an lvalue may appear as either the left-hand or right-hand side of an assignment.

2、rvalue: An expression that is an rvalue may appear on the right-hang but not left-hand side of an assignment.

Variables are lvalues and so may appear on the left-hand side of an assignment. Numeric literals are rvalues and so may not be assigned.