How do you get modf or modff to work properly? - objective-c

Question

I am simply trying to cycle through a list of (10) names using an incrementing counter by taking the modulus of the counter with respect to the length of the list. However, the code seems to skip a number here and there. I have tried both modf() and modff() and different type castings, but no luck.
Here is an example of the code:
defaultNameList = [NSArray arrayWithObjects:#"RacerX",#"Speed",#"Sprittle",#"Chim-Chim",#"Pops",#"Dale",#"Junior",#"Chip",#"Fred",#"Barney", nil];
float intpart;
int pickName = (int)(modff(entryCount/10.0,&intpart) * 10.0);
NSLog(#"%ld %f %f %f %d %#",entryCount, entryCount/10.0, modff(entryCount/10.0,&intpart), modff(entryCount/10.0,&intpart) * 10.0 ,pickName, [defaultNameList objectAtIndex:pickName]);
The console gives:
0 0.000000 0.000000 0.000000 0 RacerX
1 0.100000 0.100000 1.000000 1 Speed
2 0.200000 0.200000 2.000000 2 Sprittle
3 0.300000 0.300000 3.000000 3 Chim-Chim
4 0.400000 0.400000 4.000000 4 Pops
5 0.500000 0.500000 5.000000 5 Dale
6 0.600000 0.600000 6.000000 6 Junior
7 0.700000 0.700000 7.000000 6 Junior
8 0.800000 0.800000 8.000000 8 Fred
9 0.900000 0.900000 9.000000 8 Fred
10 1.000000 0.000000 0.000000 0 RacerX
As far as I can tell it should not skip pickName = 7 or 9, but it does.

Answer 1

Casting to (int) truncates the file. That is, if it cannot be exactly represented in the floating-point system which is used on the actual architecture, and is a bit less than the exact value, it will be rounded towards zero. To solve this problem, round the number instead of truncating:
int pickName = (int)(modff(entryCount / 10.0, &intpart) * 10.0 + 0.5);
(This assumes that the number is not negative.)
However, since you're working with integers here, and floating-point operations are expensive, you should consider using the modulo operator instead (which operates on integers):
int pickName = entryCount % 10;