Decimal ToString() conversion issue in C#

Question

I am facing a problem when I try to convert decimal? to string. Scenario is

decimal decimalValue = .1211;
string value = (decimalValue * 100).ToString();

Current Result : value = 12.1100

Expected Result : value = 12.11

Please let me know, what could be reason for this.

Answer 1

Decimal preserves any trailing zeroes in a Decimal number. If you want two decimal places instead:

decimal? decimalValue = .1211m;
string value = ((decimal)(decimalValue * 100)).ToString("#.##")

http://msdn.microsoft.com/en-us/library/0c899ak8.aspx

or

string value = ((decimal)(decimalValue * 100)).ToString("N2")

http://msdn.microsoft.com/en-us/library/dwhawy9k.aspx

From System.Decimal:

A decimal number is a floating-point value that consists of a sign, a numeric value where each digit in the value ranges from 0 to 9, and a scaling factor that indicates the position of a floating decimal point that separates the integral and fractional parts of the numeric value.

The binary representation of a Decimal value consists of a 1-bit sign, a 96-bit integer number, and a scaling factor used to divide the 96-bit integer and specify what portion of it is a decimal fraction. The scaling factor is implicitly the number 10, raised to an exponent ranging from 0 to 28. Therefore, the binary representation of a Decimal value is of the form, ((-2⁹⁶ to 2⁹⁶) / 10^{(0 to 28)}), where -2⁹⁶-1 is equal to MinValue, and 2⁹⁶-1 is equal to MaxValue.

The scaling factor also preserves any trailing zeroes in a Decimal number. Trailing zeroes do not affect the value of a Decimal number in arithmetic or comparison operations. However, >>trailing zeroes can be revealed by the ToString method if an appropriate format string is applied<<.

Remarks:

1. the decimal multiplication needs to be casted to decimal, because Nullable<decimal>.ToString has no format provider

2. as Chris pointed out you need to handle the case that the Nullable<decimal> is null. One way is using the Null-Coalescing-Operator:

   ((decimal)(decimalValue ?? 0 * 100)).ToString("N2")
   

This article from Jon Skeet is worth reading:

Decimal floating point in .NET (seach for keeping zeroes if you're impatient)