A.7.4.1 Prefix Incrementation Operators
A unary expression followed by a ++ or -- operator is a unary expression. The operand is incremented ++ or decremented -- by 1. The value of the expression is the value after the incrementation (decrementation). 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 operands and details of the operation. The result is not an lvalue.