the beginnings to a prefix notation calculator

#!/usr/bin/env rdmd

import std.stdio;
import std.conv;
import std.c.stdlib;
import std.string;
import std.array;

void main(string[] args)
{
    void usage(){writeln("Example: ^ 2 (+ 1 (+ 2 (* 2 2)))");}

    while(true)
    {
        stdout.write("> "); // print prompt
        string input = chop(stdin.readln());    // chop the new line character

        string[] temp = input.split(" ");
        real answer=0;
        bool parsing_error = false;
        while(temp.length >= 3 && !parsing_error)
        {
            auto oper = temp[$-3].removechars("()");
            //stdout.writeln("chunk: ", oper);

            real a,b;
            auto bite = temp[$-2].removechars("()");
            if((bite[0]<='9'&&bite[0]>='0')||((bite[0]=='-'||bite[0]=='.')&&bite[0]<='9'&&bite[1]>'0'))
                a = to!real(bite);
            else
            {
                parsing_error = true;
                break;
            }
            //stdout.writeln("chunk: ", bite);

            bite = temp[$-1].removechars("()");
            if((bite[0]<='9'&&bite[0]>='0')||((bite[0]=='-'||bite[0]=='.')&&bite[0]<='9'&&bite[1]>'0'))
                b = to!real(bite);
            else
            {
                parsing_error = true;
                break;
            }
            //stdout.writeln("chunk: ", bite);

            switch(oper)
            {
                case "+":
                    answer = a+b;
                    stdout.writeln("(+ ", a, " ", b, ") = ", answer);
                    break;
                case "-":
                    answer = a-b;
                    stdout.writeln("(- ", a, " ", b, ") = ", answer);
                    break;
                case "*":
                    answer = a*b;
                    stdout.writeln("(* ", a, " ", b, ") = ", answer);
                    break;
                case "/":
                    answer = a && b ? a/b : 0;
                    a && b ? stdout.writeln("(/ ", a, " ", b, ") = ", answer) : writeln("Cannot divide by zero...");
                    break;
                case "^":
                    answer = a^^b;
                    stdout.writeln("(^ ", a, " ", b, ") = ", answer);
                    break;
                case "%":
                    answer = a && b ? a%b : 0;
                    a && b ? stdout.writeln("(% ", a, " ", b, ") = ", answer) : writeln("Cannot divide by zero...");
                    break;
                default:
                    parsing_error = true;
                    break;
            }
            temp.popBack();
            temp.popBack();
            temp.popBack();
            temp ~= join([to!string(answer), ")"]);
            //stdout.writeln(temp);
            if(temp.length == 1)
            {
                temp.popBack();
                break;
            }
        }
        //stdout.writeln(temp," -> ",temp.length);
        if(parsing_error || temp.length > 0)
        {
            stdout.writeln("Invalid syntax...");
            usage();
        }
    }
}