C / C++ / MFC

 #include <iostream.h>
 #define unsafe(i)  \
         ( (i) >= 0 ? (i) : -(i) )
 
 inline
 int safe(int i)
 {
   return i >= 0 ? i : -i;
 }
  int f() {cout << "Called f()!" << endl; return 0;};
  void userCode(int x)
 {
   int ans;
   ans = unsafe(x++);   // Error! x is incremented twice
   cout << "[1] "<< x << endl;
//   ans = (f()) >= 0 ? (f()) : -(f()); 
   ans = unsafe(f());   // Danger! f() is called twice
    cout <<  "[2] "<< x << endl;

   ans = safe(x++);     // Correct! x is incremented once
      cout <<  "[3] "<< x << endl;
   ans = safe(f());     // Correct! f() is called once
      cout <<  "[4] "<< x << endl;
 } 

 void main(void)
 {
   userCode(100);
 }

[1] 102
Called f();
Called f();
[2] 102
[3] 103
Called f();
[4] 103

[1] 102
Called f();
Called f();
Called f();
Called f();
[2] 102
[3] 103
Called f();
[4] 103