Objective c division of two ints

Question

I\'m trying to produce a a float by dividing two ints in my program. Here is what I\'d expect:

1 / 120 = 0.00833

Here is the code I\'m using:

Answer 1

Do the following

float a = 1./120.

Answer 2

float a = 1/120;
float b = 1.0/120;
float c = 1.0/120.0;
float d = 1.0f/120.0f;

NSLog(@"Value of A:%f B:%f C:%f D:%f",a,b,c,d);

Output: Value of A:0.000000 B:0.008333 C:0.008333 D:0.008333

For float variable a : int / int yields integer which you are assigning to float and printing it so 0.0000000

For float variable b: float / int yields float, assigning to float and printing it 0.008333

For float variable c: float / float yields float, so 0.008333

Last one is more precise float. Previous ones are of type double: all floating point values are stored as double data types unless the value is followed by an 'f' to specifically specify a float rather than as a double.

Answer 3

In C (and therefore also in Objective-C), expressions are almost always evaluated without regard to the context in which they appear.

The expression 1 / 120 is a division of two int operands, so it yields an int result. Integer division truncates, so 1 / 120 yields 0. The fact that the result is used to initialize a float object doesn't change the way 1 / 120 is evaluated.

This can be counterintuitive at times, especially if you're accustomed to the way calculators generally work (they usually store all results in floating-point).

As the other answers have said, to get a result close to 0.00833 (which can't be represented exactly, BTW), you need to do a floating-point division rather than an integer division, by making one or both of the operands floating-point. If one operand is floating-point and the other is an integer, the integer operand is converted to floating-point first; there is no direct floating-point by integer division operation.

Note that, as @0x8badf00d's comment says, the result should be 0. Something else must be going wrong for the printed result to be inf. If you can show us more code, preferably a small complete program, we can help figure that out.

(There are languages in which integer division yields a floating-point result. Even in those languages, the evaluation isn't necessarily affected by its context. Python version 3 is one such language; C, Objective-C, and Python version 2 are not.)

Answer 4

You need to specify that you want to use floating point math.

There's a few ways to do this:

• If you really are interested in dividing two constants, you can specify that you want floating point math by making the first constant a float (or double). All it takes is a decimal point.

  float a = 1./120;
  

  You don't need to make the second constant a float, though it doesn't hurt anything.

• Frankly, this is pretty easy to miss so I'd suggest adding a trailing zero and some spacing.

  float a = 1.0 / 120;
  

• If you really want to do the math with an integer variable, you can type cast it:

  float a = (float)i/120;