iOS SDK and simple math - I know, I'm stupid

[mcannell]

I know this is stupid... very stupid....

I just want to display a percentage. How simple this should be, but my output is always 0

double actualPercentage = (4/10)*100;
NSString *finalPercent = [NSString stringWithFormat:@"%d",actualPercentage];
finalPercent = [finalPercent stringByAppendingString:@"%"];
scorePercent.text = finalPercent;

I've tried NSInteger, NSNumber, %d, %f%g

I've searched all over the internet and can't seem to find info about something so elementary

i would expect to see 40% as my output

 

[plinden]

The (4/10) is going to result in (int)4/(int)10, ie. 0.

Change it to (4./10.)*100.

 

[mcannell]

OK

my code is actually like this, how does it change what you said

double actualPercentage = (myScore/numberOfQuestions)*100;

I assume I can't just put a . after each variable

come to think of it, the myScore & numberOfQuestions are declared as NSInteger

 

[swiftaw]

what is you replace myscore by myscore*1.0, that might make the output a float rather than an integer.

 

[russellelly]

OK

my code is actually like this, how does it change what you said

double actualPercentage = (myScore/numberOfQuestions)*100;

I assume I can't just put a . after each variable

come to think of it, the myScore & numberOfQuestions are declared as NSInteger

double actualPercentage = ((double)myScore/(double)numberOfQuestions) * 100.0

should do the trick (in fact the 100 probably doesn't need a .0, but it wouldn't do any harm).

 

[mcannell]

I still get 0%

I verified that I am getting proper values for myScore & numberOfQuestions

//Display percent score in 80% format
double actualPercentage = ((double)myScore/(double)numberOfQuestions)*100.0;

NSString *finalPercent = [NSString stringWithFormat:@"%d",actualPercentage];
finalPercent = [finalPercent stringByAppendingString:@"%"];
	
scorePercent.text = finalPercent;

 

[mcannell]

ok, I changed %d to %lf and it works but instead of say 40% I get 40.0... then it runs out of space. So how do I drop all the stuff at the decimal and get 40%

Maybe double is the wrong thing

 

[mcannell]

I got it.


I changed to float and that gave me the same output as double.
So I changed the specifier to %.0f and it works

so now it looks like this

//Display percent score in 80% format
float actualPercentage = ((float)myScore/(float)numberOfQuestions)*100.0;

NSString *finalPercent = [NSString stringWithFormat:@"%.0f",actualPercentage];
finalPercent = [finalPercent stringByAppendingString:@"%"];
	
scorePercent.text = finalPercent;

 

[TonyHoyle]

You could just do the multiplication first:

(myScore*100)/numberOfQuestions

This lets you stay with integers. It's a trick worth remembering if you have to do more complex calculations, especially in time critical loops.