trouble with C# and regular expressions

Question

Hi, I am trying to use regular expression to check if a string is a number and I do not want leading zeros so "123" is legal but "0123" is not and I am using the following:
Regex objNaturalPattern = new Regex("[1-9][0-9]*");
This works fine detecting if it is a number or alpha but it always gives me true for leading zeros, how can I make the zeros in front give me a false?
Thanks

Bjarni · Answer

Thanks that worked, but now I have another question if I want the string that I am testing to be of a certain length how does that work, I was trying:
Regex regex = new Regex("^[1-9][0-9]{0,5}");
where {0,5} should allow the string to be 0 to 5 digits long but that does not work for me. Any ideas. Does anyone know of a good place to read about C# regex. It seems to me that diffrent characters have diffrent meaning in different programming languages.
BR

Mike Gold · Answer

try
Regex exp = new Regex ( "^[1-9][0-9]*" );