Obtaining float from division between NSIntegers

Question

I have two NSInteger variables called "domande" and "corrette". I have to execute this operation with them: corrette*10/domande. I want the result to be a float variable, so I declared a "voto" variable as so: "float voto = corrette*10/domande;" . When I output the value of "voto" with NSLog I get an approximated value of the result followed by ".000000".

Here's the code:

NSInteger domande = [numDomande integerValue];
NSInteger corrette = [numRisposteCorrette integerValue];
float voto = corrette*10/domande;
NSLog(@"float value is: %f", voto);

When I assign to "domande" a value of 7, and to "corrette" a value of 4: voto=5.000000 Instead it should be voto=5.71...

How can I have the division return not an integer type converted to float, but directly a float type?

score 9 · Answer 1 · answered Sep 22 '12 at 14:14

Simplest way is to do:

float voto = 10.0f * corrette / domande;

By making the first argument a float, you guarantee that the others will be promoted as well and that intermediate and final results will not suffer truncation.

You could achieve a similar result by casting corrette to a float but I tend to prefer simplicity where possible.

score 5 · Accepted Answer · answered Sep 22 '12 at 14:15

Rather than converting integers to floats, you could just get floats in the first place:

CGFloat domandeFloat = [numDomande floatValue];
CGFloat corretteFloat = [numRisposteCorrette floatValue];
CGFloat voto = (corretteFloat / domandeFloat) * 10.0f
NSLog(@"float value is: %f", voto);

score 4 · Answer 3 · answered May 08 '13 at 13:25

4

NSInteger does not have a method called floatValue. NSInteger is just an int. Instead, the solution would be:

CGFloat domandeFloat = [[NSNumber numberWithInt: numDomande] floatValue];
CGFloat domandeFloat = [[NSNumber numberWithInt: numRisposteCorrette] floatValue];
CGFloat voto = (corretteFloat / domandeFloat) * 10.0f;

answered May 08 '13 at 13:25

Rudolf J

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Actually the most correct way would be to use numberWithInteger as the source numDomande is a NSInteger, not an int – PakitoV Aug 09 '18 at 13:43

Asciiom · Answer 4 · 2012-09-22T14:15:33.133

2

Try to convert the NSIntegers to a float type first:

float voto = (float)corrette*10/(float)domande;

edited Sep 22 '12 at 14:15

answered Sep 22 '12 at 14:05

Asciiom

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[corrette floatValue] is not right - you can not send a message to not id type. Maybe you meant "(float)corrette" ? – medvedNick Sep 22 '12 at 14:11
Ah yes, I meant to cast :) I was a bit too quick. Thanks! – Asciiom Sep 22 '12 at 14:15

medvedNick · Answer 5 · 2012-09-22T14:18:28.103

0

you can cast "10" from int to float by writing it as "10.0"

  float voto = corrette*10.0/domande;

or

float voto = ((float)corrette*10) / (float)domande;

Operation "/" is returning type of it operands - 5/4 will return int result 1 because 5 and 4 are int, and 5.0/4.0 will return 1.25, because 5.0 and 4.0 are interpreted as float values. So you should manually cast type of input variables corrette and domande to float

edited Sep 22 '12 at 14:18

answered Sep 22 '12 at 14:05

medvedNick

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That's not casting 10 to a float, it's using the nearest binary representation of 10 as a floating point number. No conversion is done, and thus no cast. – Richard J. Ross III Sep 22 '12 at 14:20
well, yes, this "cast" means "change type of 10 from int to float so it will be float from the beginning" – medvedNick Sep 22 '12 at 14:25
But that's not what a cast is in C, fundamentally the two are quite different. – Richard J. Ross III Sep 22 '12 at 15:22

Obtaining float from division between NSIntegers

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