C#: Exponential Format Specifier

Question

I have a double number:

element.MaxAllowableConcLimitPpm = 0.077724795640326971;

I need to display it as

7.7725e-2

when I try to use it:

element.MaxAllowableConcLimitPpm.ToString("e4", CultureInfo.InvariantCulture)

it returns

7.7725e-002

How to say that mantissa should have one symbol instead of 3 ?

Format like this:

.ToString("0.0000e0")

returns

5.0000e2

instead of

5.0000e+2

Answer 1

You have to use a custom numeric format string - standard numeric format strings always have at least three digits in the exponent.

Example with a custom string:

using System;

public class Test
{    
    static void Main()
    {
        double value = 0.077724795640326971;
        Console.WriteLine(value.ToString("0.0000e+0")); // 7.7725e-2
    }
}

From the documentation for standard numeric format strings (emphasis mine):

The case of the format specifier indicates whether to prefix the exponent with an "E" or an "e". The exponent always consists of a plus or minus sign and a minimum of three digits. The exponent is padded with zeros to meet this minimum, if required.