Iterating through string?

You can use char.IsDigit:

    static void Main(string[] args)
    {
        var s = "IAmAString-00001";
        int index = -1;
        for (int i = 0; i < s.Length; i++)
        {
            if (char.IsDigit(s[i]))
            {
                index = i;
                break;
            }
        }
        if (index == -1)
            Console.WriteLine("digits not found");
        else
            Console.WriteLine("digits: {0}", s.Substring(index));
    }

which produces this output:

digits: 00001

string.Format and a for loop should do what you want.

for(int i = 0; i <=23; i++)
{
    string.Format("IAmAString-{0:D4}",i);
}

or something close to that (not sitting in front of a compiler).

You could use a Regex:

var match=Regex.Match("Super_Confusing-String#w00t0003",@"(?<=(^.*\D)|^)\d+$");
if(match.Success)
{
    var val=int.Parse(match.Value);
    Console.WriteLine(val);
}

To answer more specifically, you could use named groups to extract what you need:

var match=Regex.Match(
    "Super_Confusing-String#w00t0003",
    @"(?<prefix>(^.*\D)|^)(?<digits>\d+)$");

if(match.Success)
{
    var prefix=match.Groups["prefix"].Value;
    Console.WriteLine(prefix);
    var val=int.Parse(match.Groups["digits"].Value);
    Console.WriteLine(val);
}

If you can assume that the last 5 characters are the number then:

string prefix = "myprefix-";
for (int i=1; i <=23; i++)
{
  Console.WriteLine(myPrefix+i.ToString("D5"));
}

This function will find the trailing number.

private int FindTrailingNumber(string str)
{
    string numString = "";
    int numTest;
    for (int i = str.Length - 1; i > 0; i--)
    {
        char c = str[i];
        if (int.TryParse(c.ToString(), out numTest))
        {
            numString = c + numString;
        }
    }
    return int.Parse(numString);
}

Assuming all your base strings are the same, this would iterate between strings.

string s1 = "asdf123";
string s2 = "asdf127";
int num1 = FindTrailingNumber(s1);
int num2 = FindTrailingNumber(s2);

string strBase = s1.Replace(num1.ToString(), "");

for (int i = num1; i <= num2; i++)
{
    Console.WriteLine(strBase + i.ToString());
}

I think it would be better if you do the search from the last (Rick already upvoted you since it was ur logic :-))

static void Main(string[] args)
    {
        var s = "IAmAString-00001";
        int index = -1;
        for (int i = s.Length - 1; i >=0; i--)
        {
            if (!char.IsDigit(s[i]))
            {
                index = i;
                break;
            }
        }
        if (index == -1)
            Console.WriteLine("digits not found");
        else
            Console.WriteLine("digits: {0}", s.Substring(index));
        Console.ReadKey();
    }

HTH

If the last X numbers are always digits, then:

int x = 5;
string s = "IAmAString-00001";
int num = int.Parse(s.Substring(s.Length - x, x));
Console.WriteLine("Your Number is: {0}", num);

If the last digits can be 3, 4, or 5 in length, then you will need a little more logic:

int x = 0;
string s = "IAmAString-00001";
foreach (char c in s.Reverse())//Use Reverse() so you start with digits only.
{
    if(char.IsDigit(c) == false)
        break;//If we start hitting non-digit characters, then exit the loop.
    ++x;
}
int num = int.Parse(s.Substring(s.Length - x, x));
Console.WriteLine("Your Number is: {0}", num);

I'm not good with complicated RegEx. Because of this, I always shy away from it when maximum optimization is unnecessary. The reason for this is RegEx doesn't always parse strings the way you expect it to. If there is and alternate solution that will still run fast then I'd rather go that route as it's easier for me to understand and know that it will work with any combination of strings.

For Example: if you use some of the other solutions presented here with a string like "I2AmAString-000001", then you will get "2000001" as your number instead of "1".