CODEWITHSUNDEEP
c#postfix-notation
user1797574
user1797574

Reputation:

Postfix Calculator

Making a console application in C sharp to solve expressions in postfix notation by utilizing a stack, such as:

Expression: 43+2* Answer: 14

What I've done so far:

using System;
using System.Collections;
using System.Linq;
using System.Text;

namespace ConsoleApplication7
{
class Program
{
    static void Main(string[] args)
    {
        string input = "23+";
        int counter = 0;
        Stack values = new Stack();


        while (counter < input.Length)
        {
            int temp1,
                temp2,
                answer;

            char x = char.Parse(input.Substring(counter, 1));

            if (  );
            else if (x == '+')
            {
                temp1 = (int)values.Pop();
                temp2 = (int)values.Pop();

                values.Push(answer = temp1 + temp2);
            }
            else if (x == '-')
            {
                temp1 = (int)values.Pop();
                temp2 = (int)values.Pop();

                values.Push(answer = temp1 - temp2);
            }
            else if (x == '*')
            {
                temp1 = (int)values.Pop();
                temp2 = (int)values.Pop();

                values.Push(answer = temp1 / temp2);
            }
            else if (x == '/')
            {
                temp1 = (int)values.Pop();
                temp2 = (int)values.Pop();

                values.Push(answer = temp1 * temp2);
            }

            counter++;

        }
        Console.WriteLine(values.Pop());
    }
}

For the if statement, what can I use as a condition to check if x is a operand?

Upvotes: 4

Views: 5510

Answers (4)

AshleyF
AshleyF

Reputation: 3752

You could say that there essentially are no operands. Even digits can be thought of as operators that multiply the top of the stack by 10 and add the digit value; accumulating a value over several digits as necessary. Then you just need an operator for seeding this by pushing a zero to the stack (perhaps a space character for that).

http://blogs.msdn.com/b/ashleyf/archive/2009/10/23/tinyrpn-calculator.aspx

Upvotes: 0

Random Dev
Random Dev

Reputation: 52290

I really think this is more like a code review but well so be it - first: please seperate some concerns - you baked everything into a big messy monster - think about the parts of the problem and put them into seperate methods to start with.

Then: if you cannot solve the hole problem, make it smaller first: Let the user enter some kind of seperator for the parts, or assume for now that he does - space will do just fine. You can think of how to handle operators without spaces pre/postfixed later. So try parsing "2 3 +" instead of "23+" or "2 3+" ... If you do this you can indeed just use String.Split to make your life much easier!

As to how you can recognize an operant: very easy - try Double.TryParse it will tell you if you passed it a valid number and you don't have to waste your time with parsing the numbers yourself

Instead of using a while in there you should use a for or even better a foreach - heck you can even do this with LINQ and [Enumerable.Aggregate][1] and get FUNctional :D

And finally ... don't use this if/then/else mess if a switch does the job ...

Upvotes: 0

Tim S.
Tim S.

Reputation: 56556

Is your example input 2, 3, + (which equals 5), or 23, + (which is invalid input)? I'm assuming the former. How, then, would you write two-digit numbers? Your current approach doesn't seem to support this. I think you shouldn't be parsing this char-by-char, but split it into the separate components first, perhaps using a regex that recognizes numbers and punctuation. As a quick example: Regex.Matches("10 3+", @"(\d+|[\+\-\*/ ])") splits into 10, , 3, and +, which can be parsed and understood fairly easily with the code you already have, (spaces should be ignored; they're simply a punctuation I picked to separate numbers so that you can have multi-digit numbers) and int.TryParse (or double, which requires a more complicated regex pattern, see Matching Floating Point Numbers for that pattern) to see if an input is a number.

You should use a Stack<int> to avoid casting and make it compile-time safe.

Upvotes: 1

Blorgbeard
Blorgbeard

Reputation: 103525

Surely this is wrong:

((int)Char.GetNumericValue(x) <= 0 && (int)Char.GetNumericValue(x) >= 0)

I think it should be

((int)Char.GetNumericValue(x) <= 9 && (int)Char.GetNumericValue(x) >= 0)

Upvotes: 0

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