CODEWITHSUNDEEP
c#stringformat
Peter Crickman
Peter Crickman

Reputation: 25

String Format C# Small Negative Values

Why does the following program not output the negative sign for the second line?

var smallpos = 3.65433E-005;
var smallneg = -3.65433E-005;

Console.WriteLine("{0} in F4 format with a width of 8 characters {1}",
                  smallpos,
                  smallpos.ToString("F4").PadLeft(8).Substring(0, 8));

Console.WriteLine("{0} in F4 format with a width of 8 characters {1}",
                  smallneg,
                  smallneg.ToString("F4").PadLeft(8).Substring(0, 8));

Using VS 2017 Professional 15.8.2 C# 7.2

Upvotes: 0

Views: 861

Answers (2)

Kjartan
Kjartan

Reputation: 19101

Once you've eliminated enough digits from the back, the remaining number will have a value of zero, at which point the existence of a "-" has no real meaning.

This can be understood quite intuitively by running the snippet below, which has a decreasing number provided for the fixed-point specifier.

In the last line, that specifier is omitted, at that point NumberFormatInfo.NumberDecimal decides the number of decimal places used (depending on the culture used):

var smallneg = -3.65433E-005;

Console.WriteLine(smallneg.ToString("F10")); // -0,0000365433
Console.WriteLine(smallneg.ToString("F9"));  // -0,000036543
Console.WriteLine(smallneg.ToString("F8"));  // -0,00003654
Console.WriteLine(smallneg.ToString("F7"));  // -0,0000365
Console.WriteLine(smallneg.ToString("F6"));  // -0,000037
Console.WriteLine(smallneg.ToString("F5"));  // -0,00004
Console.WriteLine(smallneg.ToString("F4"));  // 0,0000 <-- Zero --> (-0) == 0

Console.WriteLine(smallneg.ToString("F"));   // 0,00

Upvotes: 1

galdin
galdin

Reputation: 14034

-3.65433E-005 represents -0.0000365433.

The issue here is with smallneg.ToString("F4"). It only considers the first 4 places after the decimal point; since they're all 0 the negative sign is left out as -0 wouldn't make much sense.

Upvotes: 3

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