Round a decimal number to the first decimal position that is not zero

Question

I want to shorten a number to the first significant digit that is not 0. The digits behind should be rounded.

Examples:

0.001 -> 0.001
0.00367 -&g         


        

Answer 1

I would declare precision variable and use a iteration multiplies that variable by 10 with the original value it didn't hit, that precision will add 1.

then use precision variable be Math.Round second parameter.

static decimal RoundFirstSignificantDigit(decimal input) {
    int precision = 0;
    var val = input;
    while (Math.Abs(val) < 1)
    {
        val *= 10;
        precision++;
    }
    return Math.Round(input, precision);
}

I would write an extension method for this function.

public static class FloatExtension
{
    public static decimal RoundFirstSignificantDigit(this decimal input)
    {
        int precision = 0;
        var val = input;
        while (Math.Abs(val) < 1)
        {
            val *= 10;
            precision++;
        }
        return Math.Round(input, precision);
    }
}

then use like

decimal input = 0.00001;
input.RoundFirstSignificantDigit();

c# online

Result

(-0.001m).RoundFirstSignificantDigit()                  -0.001
(-0.00367m).RoundFirstSignificantDigit()                -0.004
(0.000000564m).RoundFirstSignificantDigit()             0.0000006
(0.00000432907543029m).RoundFirstSignificantDigit()     0.000004