A.7.3.4 Postfix Incrementation
A postfix expression followed by a ++ or -- operator is a postfix expression. The value of the expression is the value of the operand. After the value is noted, the operand is incremented ++ or decremented -- by 1. The operand must be an lvalue; see the discussion of additive operators (Par.A.7.7) and assignment (Par.A.7.17) for further constraints on the operand and details of the operation. The result is not an lvalue.