Checking For Numeric Characters in a String Using C Sharp

Here are a number of ways you can check a string for numeric characters:

Firstly you can create a simple function like:

          public bool OnlyNumeric(string s)
          {
               int i = 0;
               while (i='0' && s[i]<='9')
                    i++;
               return i==s.Length;
          }

You could also do the check using a try/catch and if exception is thrown do whetever you do when OnlyNumeric returns.

          public bool OnlyNumeric(string s)
          {
               try
               {
                    Convert.ToInt64(s);
                    return true;
               }
               catch
               {
                    return false;
               }

          }

However with the second option exception handling is a performance expensive operation.

You could further simplify the solution by using char.IsNumber(...) in the while condition:

public bool OnlyNumeric(string s)
{
     int i = 0;
     while (i < s.Length && char.IsNumber(s[i]))
          i++;

     return i == s.Length;
}

A further option is to use regular expressions.  This regular expression ^[0-9]*$ means that:

• ^ from start of string
• [0-9] between 0-9
• [0-9]* all numbers
• $ end of string

            string[] arrNumbers = {"12aa","123","111","aaa"};
            Regex r = new Regex("^[0-9]*$");
            foreach (string a in arrNumbers)
            {
                if (r.IsMatch(a))
                {
                    Console.WriteLine("this is a Number");
                }
                else
                {
                    Console.WriteLine("This is not a Number");
                }
            }

The following regular expression pattern searches for any non numeric character and if found returns true.

    Match m;
     m = Regex.Match(inputStr, @"[^\d]+|^$");     if( m.Success )
     {
          MessageBox.Show("String was not all numeric characters");
     }
     else
     {
          MessageBox.Show("String IS ALL numeric characters");
     }

Note the use of "|^$" in the pattern is so that it will also catch an empty string.