C# Lower to Uppercase String Conversion Without Library Functions

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I have given here C# code to convert a string from lower case to uppercase characters with out using any library functions.

Source Code

using System;

using System.Collections.Generic;

using System.Text;

namespace LowerToUpper

{

   class LowerToUpper

   {

      public static String ConvertToUpperCase(String input)

      {

         String output = "";

         for (int i = 0; i < input.Length; i++)

         {

            if (input[i] >= 'a' && input[i] <= 'z')

            {

               output += (char)(input[i] - 'a' + 'A');

            }

            else

               output += input[i];

         }

         return output;

      }

      static void Main(string[] args)

      {

         System.Console.Write("Enter a string: ");

         String input = System.Console.ReadLine();

         input = ConvertToUpperCase(input);

         System.Console.WriteLine("Converted String in Upper Case: " + input);

      }

   }  

Output

Enter a string: Software and Finance

Converted String in Upper Case: SOFTWARE AND FINANCE

Press any key to continue . . .