Easiest way to truncate float to 2 decimal places?

Question

In Swift, is there a way to truncate a float to 2 decimals, such that you can perform further calculations with it? All of the threads I\'ve seen deal with casting to a str

Answer 1

You cannot round a Float or Double to 2 decimal digits exactly. The reason is that these data types use a binary floating point representation, and cannot represent numbers like 0.1 or 0.01 exactly. See for example

• Why Are Floating Point Numbers Inaccurate?
• What Every Computer Scientist Should Know About Floating-Point Arithmetic

But you said:

I need my return value to be in quarter steps (i.e. 6.50, 6.75, 5.25, etc),

and that is exactly possible because 0.25 = 2^-2 can be represented exactly as a floating point number.

The round() function rounds a floating point number to the nearest integral value. To round to the nearest quarter, you just have to "scale" the calculation with the factor 4:

func roundToNearestQuarter(num : Float) -> Float {
    return round(num * 4.0)/4.0
}

roundToNearestQuarter(6.71) // 6.75
roundToNearestQuarter(6.6)  // 6.5