Qt Code: 
  1. // A macro that returns the absolute value of i
  2.  #define unsafe(i)  \
  3.          ( (i) >= 0 ? (i) : -(i) )
  4.  
  5.  // An inline function that returns the absolute value of i
  6.  inline
  7.  int safe(int i)
  8.  {
  9.    return i >= 0 ? i : -i;
  10.  }
  11.  
  12.  int f();
  13.  
  14.  void userCode(int x)
  15.  {
  16.    int ans;
  17.  
  18.    ans = unsafe(x++);   // Error! x is incremented twice
  19.    ans = unsafe(f());   // Danger! f() is called twice
  20.  
  21.    ans = safe(x++);     // Correct! x is incremented once
  22.    ans = safe(f());     // Correct! f() is called once
  23.  }
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Can someone please tell me why x is incremented twice and f() is called twice when i use unsafe(x++) and unsafe(f()) respectively ?

I also have an other doubt also.

I build a tree from a string. For Example: "a+bc+34" or "a+2+4"

I have two classes for this.

1.Literal
2.Value

and they inherit a class called "Node" which has a variable called "type : int"

Also I have two macros

#define LITERAL_OBJECT
#define VALUE_OBJECT

which helps me to find what type of node is and then type cast and then do some operation ( addition when the two nodes under plus are numbers...etc)

I think #define's are not needed at all but I am not able to figure out how to do away with them. Can someone pls tell me how can i do things in much better way?

Thanks a lot.