Internally there was a race for the best-performing-solution on the following scenario:

A function has a string-parameter containing only digits. The function has to increment the value and return a string having the very same format.
For example: input is ’0100′ the returnvalue is ’0101′

Take this for granted:
- input is always numeric
- the incremented value will never have more chars then the input.

Requirements:
- increment the input-string by one
- padding must be dynamically, depending on the input-value (must also work for ’010′ and ’00100′)

And here is the result, starting with the fastest one:

• return (int.Parse(input) + 1).ToString().PadLeft(input.Length, ’0′);

• return (int.Parse(input) + 1).ToString(CultureInfo.InvariantCulture.NumberFormat).PadLeft(input.Length, ’0′);

• return (Convert.ToInt32(input)+1).ToString(“D” + input.Length);

And the slowest one:

• return (Convert.ToInt32(input) + 1).ToString(input.Aggregate(“”, (current, t) => current + “0″));

Summary:
- assigning values to variables is slow, so do it all within 1 line.
- using FormatProviders is slow.
- using linq is maximum slow.
- ‘Convert.ToInt32′ checks for NULL, then calls ‘int.Parse’, so better use int.Parse, if you don’t care for null.