Char.IsDigit
using System; public class CharDemo { public static void Main() { string str = "This is a test. $23"; int i; for(i=0; i < str.Length; i++) { Console.Write(str[i] + " is"); if(Char.IsDigit(str[i])) Console.Write(" digit"); if(Char.IsLetter(str[i])) Console.Write(" letter"); if(Char.IsLower(str[i])) Console.Write(" lowercase"); if(Char.IsUpper(str[i])) Console.Write(" uppercase"); if(Char.IsSymbol(str[i])) Console.Write(" symbol"); if(Char.IsSeparator(str[i])) Console.Write(" separator"); if(Char.IsWhiteSpace(str[i])) Console.Write(" whitespace"); if(Char.IsPunctuation(str[i])) Console.Write(" punctuation"); Console.WriteLine(); } Console.WriteLine("Original: " + str); // Convert to upper case. string newstr = ""; for(i=0; i < str.Length; i++) newstr += Char.ToUpper(str[i]); Console.WriteLine("Uppercased: " + newstr); } }