reading individual "words" from a buffered input

using System.Linq;

namespace Icod.TestRig {

    public static class Program {

        [System.STAThread]
        public static System.Int32 Main( System.String[] args ) {

            var line = System.Console.In.ReadLine().TrimToNull();
            while ( !System.String.IsNullOrEmpty( line ) ) {
                foreach ( var word in ReadWord( line ) ) {
                    System.Console.Out.WriteLine( word );
                }
                line = System.Console.In.ReadLine().TrimToNull();
            }

            System.Console.Error.WriteLine( "(Strike any key to exit.)" );
            System.Console.ReadKey( true );
            return 0;
        }

        public static System.String TrimToNull( this System.String @string ) {
            if ( System.String.IsNullOrEmpty( @string ) ) {
                return null;
            }
            @string = @string.Trim();
            if ( System.String.IsNullOrEmpty( @string ) ) {
                return null;
            }
            return @string;
        }

        public static System.Collections.Generic.IEnumerable<System.String> ReadWord( System.String input ) {
            input ??= System.String.Empty;

            var inlen = input.Length;
            System.Int32 start = 0;
            System.Int32 stop;
            do {
                while (  ( start < inlen ) && System.Char.IsWhiteSpace( input[ start ] ) ) {
                    start++;
                }
                stop = start;
                while ( ( stop < inlen ) && !System.Char.IsWhiteSpace( input[ stop ] ) ) {
                    stop++;
                }
                if ( start == stop ) {
                    yield break;
                } else {
                    yield return input.Substring( start, stop - start );
                }
                start = stop;
            } while ( start < inlen );

            yield break;
        }

    }

}