Testé avec Visual C++ 6 :

#include <stdio.h>

int main(int argc, char* argv[])
{
   int x, z;
   x = 1; z = 0;
   printf("x = %d | z = %d\n", x, z);
   z = (x++) + (x++);
   printf("x = %d | z = %d\n", x, z);

   z = x++ + x++;
   printf("x = %d | z = %d\n", x, z);

   z = x + (x++);
   printf("x = %d | z = %d\n", x, z);

   z = x + x++;
   printf("x = %d | z = %d\n", x, z);


   return 0;
}

donne

x = 1 | z = 0
x = 3 | z = 2
x = 5 | z = 6
x = 6 | z = 10
x = 7 | z = 12
Press any key to continue

et 0 erreurs, 0 warnings

(enfin si 2 :

Compiling...
StdAfx.cpp
Compiling...
test.cpp
C:\dev\test\test.cpp(9) : warning C4100: 'argv' : unreferenced formal parameter
C:\dev\test\test.cpp(9) : warning C4100: 'argc' : unreferenced formal parameter
Linking...

test.exe - 0 error(s), 2 warning(s)

Avec optimisations (max speed):

x = 1 | z = 0
x = 3 | z = 2
x = 5 | z = 6
x = 6 | z = 10
x = 7 | z = 12
Press any key to continue

Avec optimisation (Min Size):

x = 1 | z = 0
x = 3 | z = 2
x = 5 | z = 6
x = 6 | z = 10
x = 7 | z = 12
Press any key to continue

Toutes optimisations :

x = 1 | z = 0
x = 3 | z = 2
x = 5 | z = 6
x = 6 | z = 10
x = 7 | z = 12
Press any key to continue

(j'ai presque l'impression de me repeter..)