l value required as increment operand

Question

Can somebody explain the compilation error in the program

#include<stdio.h>
int main()
{
   int i = 10;
   printf("%d", ++(-i));
   return 0;
}

`++(-i)` => `++(-10)` : It is not possible to assign the result of the increment to -10. — BLUEPIXY, Aug 24 '14 at 15:50
It's interesting how this question is an almost _exact_ duplicate to [this question](http://stackoverflow.com/questions/6230274/lvalue-required-as-increment-operand-error)… except that it's ported from C++ to C. — DarkDust, Aug 24 '14 at 15:51

score 1 · Accepted Answer · answered Aug 24 '14 at 15:49

The result of -i is an r-value, not an l-value. You can't increment r-values with the ++ or -- operators; you can only increment an l-value.

Roughly, an l-value could appear on the LHS (left-hand side) of an assignment. You could not write:

-i = -i + 1;

For the same reason, you cannot write ++(-i).

1 Answers1