using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Scanner scanner = new Scanner();

        List<Token> tokens = scanner.Scan("12375 + 234 / 88");

​

        // For now, just print the tokens.

        foreach (var token in tokens) {

            Console.WriteLine(token);

        }

    }

}

​

public enum TokenType{

​

    NUMBER,

    ADDITION, SUBTRACTION, DIVISION, MULTIPLICATION

​

};

​

public class Token{

    public TokenType Type;

    public string Lexeme;

    public Token(string lexeme, TokenType type) {

        Type = type;

        Lexeme = lexeme;

    }

    public override string ToString() {

        return Lexeme + " as " + Type.ToString();   

    }

}

​

public class Scanner{

    int current;

    int start;

    string content;

    List<Token> tokens;

    public List<Token> Scan(string ogcontent){

        current = 0;

        start = 0;

        content = ogcontent;

        tokens = new List<Token>();

        // read tokens while we can...

        while(!IsAtEnd()){

            start = current;

            switch(content[current]){

                case '+' : tokens.Add(new Token("+", TokenType.ADDITION)); break;

                case '-' : tokens.Add(new Token("-", TokenType.SUBTRACTION)); break;

                case '*' : tokens.Add(new Token("*", TokenType.MULTIPLICATION)); break;

                case '/' : tokens.Add(new Token("/", TokenType.DIVISION)); break;

                case ' ' :

                case '\n' :

                case '\t' :

                    break;

                default :

                    if(IsNumeric(content[current])) {

                        HandleNumber();

                        break;

                    }else if (IsAlpha(content[current])) {

                        HandleIdentifier ();

                        break;

                    }else

                        throw new ArgumentException("Unexpected character " + content[current]);

            }

            current++;

        }

        return tokens;

    }

    private bool IsAtEnd() {

        if(current == content.Length)

            return true;

        return false;   

    }

    private void HandleNumber(){

         // TODO handle decimals

        // look ahead for more numbers

        while (true){

            if(current < content.Length-1 && IsNumeric(content[current+1]))

                current++;

            else

                break;

        }

        tokens.Add(new Token(content.Substring(start, current-start+1), TokenType.NUMBER));

    }

    private void HandleIdentifier(){

         // TODO implement

    }

    private bool IsNumeric(char c) {

        if(c >= '0' && c <= '9')

            return true;

        return false;

    }

    private bool IsAlpha(char c) {

         // TODO implement

        return false;

    }

}

​

​