RGB Colours.

[Jekate]

I know there are already threads on RGB colours but there is something that is really bugging me. I've looked over this many times and so have my friends but we can't figure it out. Here is the code :

code:

var col1 : real var colchange : int col1 := 0 loop     if col1 = 1 then         colchange := 1     elsif col1 = 0 then         colchange := 0     end if     if colchange = 1 then         col1 := col1 - 0.01     elsif colchange = 0 then         col1 := col1 + 0.01     end if     RGB.SetColor (1, col1, 0, 0)     drawfillbox (0, 0, 100, 100, 1)     delay (10) end loop

The program is suppose to draw the box so it turns from black to red slowly. It does that properly but then it is suppose to do the same back to black.

It is probably some stupid mistake. Thnx.

[beard0]

I have not fixed your code, but simply added two lines that will show you what your problem is so that you can fix your code yourself. The technique I have used here is a very useful one that you should start using yourself to debug your programs.

code:

var col1 : real var colchange : int col1 := 0 loop     if col1 = 1 then         colchange := 1     elsif col1 = 0 then         colchange := 0     end if     if colchange = 1 then         col1 := col1 - 0.01     elsif colchange = 0 then         col1 := col1 + 0.01     end if     RGB.SetColor (1, col1, 0, 0)     drawfillbox (0, 0, 100, 100, 1)     delay (10)     locate (1, 1)                    %My debugger     put "col1: ", col1               %   lines end loop

[Jekate]

I get what your showing but the program still isn't working as it should. I have:

code:

if col1 = 1 then colchange := 1 end if

and then

code:

if colchange = 1 then col := col - 0.01 end if

This should make col1 decrease once it reaches 1 but it is not for some reason. I think that it is skipping 1 for unknown causes. I fixed the program though by adding >= and <= to it. Here it is:

code:

var col1 : real var colchange : int col1 := 0 loop     if col1 >= 1 then         colchange := 1     elsif col1 <= 0 then         colchange := 0     end if     if colchange = 1 then         col1 := col1 - 0.01     elsif colchange = 0 then         col1 := col1 + 0.01     end if     RGB.SetColor (1, col1, 0, 0)     drawfillbox (0, 0, 100, 100, 1)     delay (10) end loop

[beard0]

The problem you were having comes from the fact that 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + .... + 0.01 does not equal 1 in Turing, and many other languages, as it is stored in binary, and so there are actually roudning errors: 0.01 base ten in binary is 0.000000101000111101011100001010001111010111000010100011110101... This was actually already discussed here in detail. The proper way to check if two real numbers are "equal" is to use

code:

abs(a-b)<tolerance