Assignment is performed with the operator =. It means “Take the right-hand side (often called the rvalue) and copy it into the left-hand side (often called the lvalue).” An rvalue is any constant, variable, or expression that can produce a value, but an lvalue must be a distinct, named variable (that is, there must be a physical space in which to store data). For instance, you can assign a constant value to a variable (A = 4;), but you cannot assign anything to constant value – it cannot be an lvalue (you can’t say 4 = A;).