Do - While now i am Logically Stuck - objective-c

Question

I am proper confused.com now and my lack of programming knowledge is clearly showing... so time to call in the pro's! (as a side note i do feel that i have learned a great deal already from you all)
The Problem
I have a little app that takes the width of a virtual wall then asks for the tile size, it then works out how many tiles you can fit with no gap between the width, if the tiles do not fit equally the user is presented with two buttons "grow wall" or "shrink wall", in this example the code below if for growing the wall. It should then run through the while trying to find out in increments of 0.1 how wide the wall needs to be to allow the tiles to fit exactly. It needs to be able to handle double values such as the wall being 12.5 feet wide with a tile width and length 13.6 that is why i am using doubles not ints
I have the following code (but think i am simplifying this way too much)
either way it is not working i have spent half a day reading playing etc but can't figure it out, am i going down the wrong road or am i on the correct track
As always any advice would be warmly received
Mr H
{
double wWdth;
double tWdth;
double wdivision = 3;
NSString *growstring = [NSString stringWithFormat:#"%#,%#", self.wallWidth.text, self.tileWidth.text];
NSArray *wall = [growstring componentsSeparatedByString:#","];
NSLog(#"%#",wall);
wWdth = [[wall objectAtIndex:0]doubleValue];
blkWdth = [[wall objectAtIndex:1]doubleValue];
do
{
NSLog(#" INSIDE WHILE %.f",wdivision);
wWdth = wWdth;
wWdth += 0.1;
wdivision = fmod(qWdth,blkWdth);
} while (wdivision ==! 0);
NSString* newWdth = [NSString stringWithFormat:#"%.f", wWdth];
self.wallWidth.text=newWdth;
}

Answer 1

Your while loop condition has several problems. It is based on the value of wdivision and the value of wdivision is from fmod(qWdth,blkWdth). But neither qWdth nor blkWdth ever change. So your loop will either execute once or forever.
Your loop condition needs to be based on a value that will eventually become false so the loop terminates at some point.
Also, you are using ==! for (what I assume) to be the "not equal" operator. The "not equal" operator is !=. What you have is really:
while (wdivision == !0);
and !0 equates to 1 so you really have:
while (wdivision == 1);
So your loop will end after one iteration unless is just so happens that wdivision is equal to 1. And if it is, your loop will never end.
Since wdivision is a double based on the fmod function, it may never actually equal 0 exactly. You should probably use this instead:
while (division > DBL_EPSILON);
But again, you need to change how wdivision is calculated so it is different each iteration.

Answer 2

If you want to stick with the code you have, recognize that "getting within half of the increment" is as close as you can get. So the lines
wWdth += 0.1;
wdivision = fmod(qWdth,blkWdth);
} while (wdivision ==! 0);
Should be replaced with
wWdth += increment;
wdivision = fmod(qWdth,blkWdth);
} while (abs(wdivision) > 0.5*increment);

Answer 3

Maybe I'm not understanding the question completely correctly, so I apologize if I don't. You say you ask for a tile size right? And then you grow/shrink the wall if the tiles can't fit perfectly into that wall size? If so, can't you just take the current wall size and set it to the next multiple (up or down) of the tile size based on when you click grow/shrink wall? Setting it to a multiple of the tile size will allow for the tiles to fit exactly in it.