Question

A weird thing happened when I tried to add 4 decimals (demanded in solution) to a 2-decimal double value:

Incorrect value:

    var result = string.Format("{0:#,0.0000}", Math.Truncate(2.03*10000)/10000);

//Returns 2.0299

Correct values:

    var result = string.Format("{0:#,0.0000}", Math.Truncate(2.02*10000)/10000);

//Returns 2.0200

And:

    var result = string.Format("{0:#,0.0000}", Math.Truncate(2.04*10000)/10000);

//Returns 2.0400

Any idea why this happens ONLY to 2.03? 12.03 as input value returns 12.0300 btw.

I am lost. Please help.

Answer 1

There is no point multiplying by 10000 and dividing by 10000 here. You only risk introducing slight errors, like what you see here: note that doubles and floats use a base-2 representation and hence cannot exactly represent arbitrary decimal numbers.

This will give you what you want:

String.Format("{0:#,0.0000}", 2.03)

If you require perfect accuracy with decimal numbers, use the decimal type instead.