Strange behavior outcome if-statement - objective-c

Question

I have the following code:
- (NSArray *)checkNormalGameDuelAndMatch:(float)nrDuelQs andNrQPerDuel:(float)nrQPerDuel andNrMatchQ:(float)nrMatchQ andActivePlayer:(float)actPlayerNrQ andInactivePlayer:(float)inactivePlayerNrQ {
NSLog(#"checkNormalGameDuelAndMatch:");
// Check for Matches and Duels to prep for swaps and/or match endings
NSArray *theCheckArray = [[NSArray alloc]init];
NSLog(#"nrDuelQs: %.0f / nrQPerDuel: %.0f", nrDuelQs, nrQPerDuel);
// Check if Match still on
NSLog(#"actPlayerNrQ: %.0f / inactivePlayerNrQ: %.0f / nrMatchQ: %.0f", actPlayerNrQ, inactivePlayerNrQ, nrMatchQ);
if (actPlayerNrQ < nrMatchQ && inactivePlayerNrQ < nrMatchQ) {
// Match is still on
_isMatchStillOn = YES;
// Check if Duel is till on
if (nrDuelQs < nrQPerDuel) {
// Duel is still on
_isDuelStillOn = YES;
NSLog(#"_isDuelStillOn = YES;");
}
else {
_isDuelStillOn = NO;
NSLog(#"_isDuelStillOn = NO;");
}
}
else {
//==MATCH IS OVER==//
_isMatchStillOn = NO;
NSLog(#"MATCH OFF");
}
theCheckArray = #[[NSNumber numberWithBool:_isDuelStillOn], [NSNumber numberWithBool:_isMatchStillOn]];
return theCheckArray;
}
With the following NSLog output, during two loops:
checkNormalGameDuelAndMatch:
nrDuelQs: 4 / nrQPerDuel: 5
actPlayerNrQ: 4 / inactivePlayerNrQ: 0 / nrMatchQ: 5
_isDuelStillOn = YES;
checkNormalGameDuelAndMatch:
nrDuelQs: 5 / nrQPerDuel: 5
actPlayerNrQ: 5 / inactivePlayerNrQ: 0 / nrMatchQ: 5
MATCH OFF
I guess there is something wrong with the If-statement and "&&" as i am not expecting the "MATCH OFF" when it comes.
I guess i am blind as this should not be complicated.

Answer 1

This is very likely happening because the variables are of the type float: even through they both print as 5, one of them may be actually slightly smaller than the other (say, 4.9999999999999999). This could happen because of the way actPlayerNrQ is calculated: for example, if you add 0.1 fifty times, you would not get exactly a 5.
Here is a link to an example (it is in C, but that part of the language is shared with Objective C).
float n = 0;
int i = 0;
for (i = 0 ; i != 25 ; i++, n += 0.2);
printf("%f < 5.000000 : %s", n, n < 5.0 ? "yes":"no");
This prints
5.000000 < 5.000000 : yes
To fix this, you could compare with an epsilon, for example
#define EPSILON 1E-8
// 1E-8 stands for 1*10^-8, or 0.00000001
...
if ((actPlayerNrQ - nrMatchQ) < EPSILON && (inactivePlayerNrQ - nrMatchQ) < EPSILON)
...