Regex accept numeric only. First character can't be 0

Question

I have a textbox that I created using .NET..

By using that textbox, the user only can key in numeric. But not start with 0. start with 1-9. after the user key in the 1-9 at the first character, the user can key in 0.

Regex reg = null;
reg = new System.Text.RegularExpressions.Regex("^[1-9][0-9]*$")
return reg.IsMatch(str);

That is my regex expression. By using that i can't key in 1-9. but only 0 and alphabet. But if i using ^[1-9] I can key in numeric, but can't key in the 0.

I already tried all the answer that all of you suggest. But still can't work. It's not like i dont read all of your answer.

here is the picture..

I want to validate at the first time, the user only can key in numeric, but start with value that is not 0 or alphabet but 1-9. After the first character, user may only key in 0-9.

i do use Int.TryParse, but i use that after i hit a button to process.

reg = new System.Text.RegularExpressions.Regex("^[^0-9]");

that regex accept only numeric from 0 to 9.

reg = new System.Text.RegularExpressions.Regex("^[^1-9]");

that regex accept only numeric from 1 to 9.

How can i add more expression to regex for the second character until the rest that only accept numeric 0-9?

By the way, i don't care about 0.99 because in here, the price is fix. not with 0.99 or 0.123..

Any others way to do it? thanks.

Answer 1

If you're looking at something like a price, you need to consider that 0.99 is probably perfectly valid. For something like that, I would simply start with a non-complex ^[0-9]*(\.[0-9]{0,2})?$ (again there may be edge cases that may make it more complex like three digits after the decimal point and so on) and allow leading zeroes, since they don't "damage" the value in anyway.

It it must start with a non zero, just change the initial [0-9]* to a [1-9][0-9]*. For integers only (as seems to be indicated by your added sample data), that would be:

^[1-9][0-9]*$

Answer 2

To match a number starting with any digit but zero:

^[1-9][0-9]*$

And if you want to match 0 as well:

^([1-9][0-9]*)|([0]+)$

remove the last plus if you want a single zero only

To allow any alpha-numeric after first non-zero:

^[1-9a-zA-Z][0-9a-zA-Z]*$

Answer 3

As your code is .NET you should not use regex to parse an Integer. Just use UInt32.TryParse() method

uint num=0;
if(UInt32.TryParse(str, out num)){
    Console.WriteLine("Converted '{0}' to {1}.", str, num);   
}else{
    Console.WriteLine("conversion of '{0}' failed.", value==null? "": value);
}

Old answer

This simple regular expression will do it ^[1-9]\d*$

Answer 4

This is what worked the best for me:

^(?!(0))[0-9]$