Wrong #defined calculated value

[programandala.net]

I think there's something I'm missing about the way #define values are calculated, look:

Code:

#define screenFirstCol 0 #define screenLastCol 31 #define borderFirstCol screenFirstCol #define borderLastCol screenLastCol #define oWinFirstCol borderFirstCol+1 #define oWinLastCol borderLastCol-1 ' Wrong result, 32 instead of 30: #define oWinWidth oWinLastCol-oWinFirstCol+1 cls print "Expected values in cramps:" print print "screenFirstCol(0)=";screenFirstCol print "screenLastCol(31)=";screenLastCol print "borderFirstCol(0)=";borderFirstCol print "borderLastCol(31)=";borderLastCol print "oWinFirstCol(1)=";oWinFirstCol print "oWinLastCol(30)=";oWinLastCol ' Wrong result, 32 instead of 30: print "oWinWidth(30)=";oWinWidth pause 0 stop

What's the problem?

I think #defined values are simple labels calculated by the preprocessor. Is it right? Is there any limit about the depth of the calculated values?

[britlion]

Not sure what's going on there. I get the same result.

It can't be because it's three things -

Code:

#define test 1+2+3 print test

comes back with 6, correctly.

The ic basically shows "print 32" as that last line that should be 30, so I can't easily drill down any further - the preprocessor is definitely making that set into a 32 though.

[boriel]

I think there's something I'm missing about the way #define values are calculated, look:

Code:

#define screenFirstCol 0 #define screenLastCol 31 #define borderFirstCol screenFirstCol #define borderLastCol screenLastCol #define oWinFirstCol borderFirstCol+1 #define oWinLastCol borderLastCol-1 ' Wrong result, 32 instead of 30: #define oWinWidth oWinLastCol-oWinFirstCol+1

Let me check it:

• borderFirstCol == 0
  
• borderLasCol == 31
  
• oWinFirstCol == 0 + 1 // Note: always expanded
  
• oWinLastCol == 31 - 1
  
• oWinWidth == 31 - 1 - 0 + 1 + 1 // This is the defined result

So oWinWidth == 32
Try using parenthesis in the #defines. The preprocessor does not calculate, just replace labels with code. With parenthesis:

Code:

#define screenFirstCol 0 #define screenLastCol 31 #define borderFirstCol screenFirstCol #define borderLastCol screenLastCol #define oWinFirstCol (borderFirstCol+1) #define oWinLastCol (borderLastCol-1) ' Wrong result, 32 instead of 30: #define oWinWidth (oWinLastCol-oWinFirstCol+1)

This gives oWinWidth == ((31 - 1) - (0 + 1) + 1) which effectively is reduced to 30.
This also happens in C.

I think #defined values are simple labels calculated by the preprocessor. Is it right? Is there any limit about the depth of the calculated values?

No limit (only available memory).

[programandala.net]

The preprocessor does not calculate, just replace labels with code. With parenthesis:

I see. The label is not replaced by the calculation, but by its raw content. Thank you.