Question

I am developing an app and want to round off values
i.e if the output is 4.8 I want to display 4.8
while if the output is 4.0 , I want to display 4

Also, it would be great if I could precisely round values : as in if value is 4.34 then round to 4.3 while if its 4.37 then round it to 4.4

Answer 1

One way to round floating point values is to just add 0.5 and then truncate the value.

double valueToRound = GetTheValueFromSomewhere();
double roundedValue = (double)((int)(valueToRound + 0.5));

This will round 1.4 down to 1.0 and 1.5 up to 2.0 for example. To round to other decimal places as you mentioned, simply multiply the initial value by 10, or 100, etc. use the same sort of code, and then divide the result by the same number and you’ll get the same result at whatever decimal place you want.

Here’s an example for rounding at an arbitrary precision.

double valueToRound = GetTheValueFromSomewhere();
int decimalPrecisionAtWhichToRound = 0;
double scale = 10^decimalPrecisionAtWhichToRound;
double tmp = valueToRound * scale;
tmp = (double)((int)(tmp + 0.5));
double roundedValue = tmp / scale;

So, if decimalPrecisionAtWhichToRound is set to 0 as in the above it’ll round to the nearest whole integer. 1.4 will round to 1.0. 1.5 will round to 2.0.

If you set decimalPrecisionAtWhichToRound to 1, it would round to the nearest tenth. 1.45 would round to 1.5 and 1.43 would round to 1.4.