Most efficient way to convert a string to 2 decimal places in C#

I have a string which needs a decimal place inserted to give a precision of 2.

3000 => 30.00
 300 =>  3.00
  30 =>   .30

From stackoverflow

• Given a string input, convert to integer, divide by 100.0 and use String.Format() to make it display two decimal places.

  String.Format("{0,0:N2}", Int32.Parse(input) / 100.0)
  

  Smarter and without converting back and forth - pad the string with zeros to at least two characters and then insert a point two characters from the right.

  String paddedInput = input.PadLeft(2, '0')
  
  padedInput.Insert(paddedInput.Length - 2, ".")
  

  Pad to a length of three to get a leading zero. Pad to precision + 1 in the extension metheod to get a leading zero.

  And as an extension method, just for kicks.

  public static class StringExtension
  {
    public static String InsertDecimal(this String @this, Int32 precision)
    {
      String padded = @this.PadLeft(precision, '0');
      return padded.Insert(padded.Length - precision, ".");
    }
  }
  
  // Usage
  "3000".InsertDecimal(2);
  

  Note: PadLeft() is correct.

  PadLeft()   '3' => '03' => '.03'
  PadRight()  '3' => '30' => '.30'
  

  Samuel : He said the input is a string, not an integer.

  Murtaza RC : works like a charm ! thanks a lot

  Murtaza RC : well I can convert it to an int :)

  Samuel : Then you really should say that.

  Murtaza RC : There - you have your answer ...convert the string to int :)

  Daniel Brückner : Parsing if not required and converting back is not smart ... ^^

• Use tryParse to avoid exceptions.

  int val;
  
  if (int.Parse(input, out val)) {
      String.Format("{0,0:N2}", val / 100.0);
  }
  

  Samuel : You don't have to cast to double if one side is already double. It will cast to double automatically.

• here's very easy way and work well.. urValue.Tostring("F2")

  let say.. int/double/decimal urValue = 100; urValue.Tostring("F2"); result will be "100.00"

  so F2 is how many decimal place u want if you want 4 place, then use F4