How does a computer represent a "5" in its memory?  
      EVERYTHING is stored as a binary code (1s and 0s).
      But, there are MANY codes...
      --------------------------
      ASCII character:          0011 0101
      UTF-8 unicode:            0011 0101 (same as ASCII in 8 bits)
      Unsigned decimal(8 bits): 0000 0101        
      Signed decimal(8):        0000 0101 (same as unsigned for a positive #)    
      Unsigned decimal(16):     0000 0000 0000 0101
      Unsigned decimal(32):     0000 0000 0000 0000 0000 0000 0000 0101
      Floating Point (float):   0100 0000 1010 0000 0000 0000 0000 0000
      Double (double):          0100 0000 0001 0100 0000 0000 0000 0000
                                0000 0000 0000 0000 0000 0000 0000 0000
      

      This is why, whe reading in a number from the keyboard, a conversion must 
      take place. Sometimes the conversion is explicit and sometimes it is implicit.

      int i;
      double d;
      string s;

      // input the number - convert from string to 'number'
      Console.Write( "Enter a number: " );
      s = Console.ReadLine( );
      i = int.Parse( s );
      d = double.Parse( s );

      // output the number - convert number back to string
      Console.WriteLine( s );
      Console.WriteLine( i.ToString( ) );
      Console.WriteLine( d.ToString( ) );

      or more simply...
                        i = int.Parse( Console.ReadLine() );
                        d = double.Parse( Console.ReadLine() );