String mathematical input and solution

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suppose I have to accept an mathematical expression in a string format from the user, like e.g. 2*5 or 9/5+9 or 91-10+82/3 and so on. It can be of any length. It works if I have single length operand like 3+9-5*4/2 by some change in my below code it works fine. but fails if i give it more then one length operand like 38+12/2-7+69 or 325-69+584 and so on C#.

What I have tried:

C#

Below code works fine for single length operand.

    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;

    namespace ConsoleApplicationExpressionFirstDay
    {
    class Program
    {
        static void Main(string[] args)
        {
            char[] arrOne = new char[100];
            int[] arrTwo = new int[2];
            string opr="+";
            string input;
            int j = 0;
            int i = 0;
            input = Console.ReadLine();
            arrOne = input.ToCharArray();
            for (i = 0; i &lt; arrOne.Length; i++)
            {
                
                    if (arrOne[i] &gt;= 48 &amp;&amp; arrOne[i] &lt;= 57)
                    {
                            arrTwo[j] = Convert.ToInt32(char.ConvertFromUtf32(arrOne[i]));
                            j++;

                    }
                    else
                    {
                        opr =char.ConvertFromUtf32(arrOne[i]);
                    }

                if (j == 2){
                    switch (opr)
                    {
                        case "+":
                            arrTwo[0] = arrTwo[0] + arrTwo[1];
                            j = 1;
                            break;
                        case "-":
                            arrTwo[0] = arrTwo[0] - arrTwo[1];
                            j = 1;
                            break;
                        case "*":
                            arrTwo[0] = arrTwo[0] * arrTwo[1];
                            j = 1;
                            break;
                        case "/":
                            arrTwo[0] = arrTwo[0] / arrTwo[1];
                            j = 1;
                            break;
                        default:
                            j = 0;
                            break;
                    }
                }
            }
            Console.WriteLine("Result : " + arrTwo[0]);
            Console.ReadLine();

        }
    }
    }


But this code fails for more than one length operands

    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;

    namespace ConsoleApplicationExpressionFirstDay
    {
    class Program
    {
        static void Main(string[] args)
        {
            char[] arrOne = new char[100];
            int[] arrTwo = new int[2];
            string opr="+";
            string input;
            int j = 0;&lt;pre lang="c#"&gt;int concat = 0;
            int i = 0;
            input = Console.ReadLine();
            arrOne = input.ToCharArray();
            for (i = 0; i &lt; arrOne.Length; i++)
            {
                
                    if (arrOne[i] &gt;= 48 &amp;&amp; arrOne[i] &lt;= 57)
                    {
                        if (concat == 0)
                        {
                            arrTwo[j] = Convert.ToInt32(char.ConvertFromUtf32(arrOne[i]));
                            j++;
                            concat++;
                        }
                        else
                        {
                            j = 1;
                            arrTwo[j] = Convert.ToInt32(Convert.ToString(arrTwo[1])+char.ConvertFromUtf32(arrOne[i]));
                            j++;
                            concat = 0;
                        }

                    }
                    else
                    {
                        opr =char.ConvertFromUtf32(arrOne[i]);
                        concat = 0;
                    }

                if (j == 2&amp;&amp;concat==0){
                    switch (opr)
                    {
                        case "+":
                            arrTwo[0] = arrTwo[0] + arrTwo[1];
                            j = 1;
                            break;
                        case "-":
                            arrTwo[0] = arrTwo[0] - arrTwo[1];
                            j = 1;
                            break;
                        case "*":
                            arrTwo[0] = arrTwo[0] * arrTwo[1];
                            j = 1;
                            break;
                        case "/":
                            arrTwo[0] = arrTwo[0] / arrTwo[1];
                            j = 1;
                            break;
                        default:
                            j = 0;
                            break;
                    }
                }
            }
            Console.WriteLine("Result : " + arrTwo[0]);
            Console.ReadLine();

        }
    }
    }

Posted 28-Oct-16 20:54pm

Akhilesh Chauhan

Updated 4-Nov-16 18:39pm

v7

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Comments

Karthik_Mahalingam 3-Nov-16 0:35am

check this
http://www.codeproject.com/Articles/17853/Implementing-an-Excel-like-formula-engine

Richard MacCutchan 4-Nov-16 6:50am

You have not explained where the problem occurs in your code. You need to process each pair of numbers in turn, depending on the priority of the operator.

Akhilesh Chauhan 4-Nov-16 6:53am

I just simply want to evaluate my expression from first element No need for priority. thanks

Richard MacCutchan 4-Nov-16 6:55am

That does not alter what you need to do.

Richard MacCutchan 4-Nov-16 6:53am

Your input parsing does not look very good. You need to extract each number and each operand into separate strings before converting them into integers. Once you have done that you can perform the actual calculations.

Akhilesh Chauhan 4-Nov-16 7:02am

I have one variable to extract operator "opr" and an array "arrTwo" of two packet to store two different operands for each time.

Richard MacCutchan 4-Nov-16 7:19am

But your parsing is not flexible. When extracting numbers it would be better to copy from the input string to a separate string all digits until you reach an operator (or end of input) . Do the same for the second number. Only then should you convert those substrings into integers and calculate the total based on the operator.

Richard MacCutchan 4-Nov-16 7:00am

See also https://en.wikipedia.org/wiki/Reverse_Polish_notation.

Philippe Mori 5-Nov-16 11:11am

Uses a debugger to understand why your program does not works. Once you have understand that, then design a program that might works.

By the way, it would be a good idea to start by writing a class that would be used for parsing and would be able to read token one by one. For example, if you have 3 consecutives digits, they should be handled as a single number.

Another more important problem with your code is that it does not respect operator precedence. Multiplying should be done before addition.

As suggested in solution 1, your are better to find information on the web... Making your own parser using only C# code your write yourself does not make much sense as it is a lot of works while there are lexer and parser already made .

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OriginalGriff · Accepted Answer · 2016-10-28T21:02:00

Google is your friend: Be nice and visit him often. He can answer questions a lot more quickly than posting them here...

A very quick search would have found you loads of examples. c# evaluate expression - Google Search[^] gives you 88,000 examples ...

Here's a good example: State of the Art Expression Evaluation[^]

In future, please try to do at least basic research yourself, and not waste your time or ours.

Akhilesh Chauhan · Accepted Answer · 2016-11-04T18:39:00

C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplicationExpressionUsingWhileLoop
{
class Program
{
    static void Main(string[] args)
    {
        char[] arrOne = new char[100];
        int[] arrTwo = new int[2];
        string opr = " ";
        string input;
        int j = 0;
        int i = 0;
        input = Console.ReadLine();
        arrOne = input.ToCharArray();
        for (i = 0; i < arrOne.Length; i++)
        {

            while(arrOne[i] >= 48 && arrOne[i] <= 57)
            {
                arrTwo[j] = Convert.ToInt32(Convert.ToString(arrTwo[j]) + char.ConvertFromUtf32(arrOne[i]));
                if (i == (arrOne.Length)-1)
                {
                    break;
                }
                else
                {
                    i++;
                }
            }
                j++;
                if (j == 2)
                {
                    switch (opr)
                    {
                        case "+":
                            arrTwo[0] = arrTwo[0] + arrTwo[1];
                            j = 1;
                            arrTwo[1] = 0;
                            break;
                        case "-":
                            arrTwo[0] = arrTwo[0] - arrTwo[1];
                            j = 1;
                            arrTwo[1] = 0;
                            break;
                        case "*":
                            arrTwo[0] = arrTwo[0] * arrTwo[1];
                            j = 1;
                            arrTwo[1] = 0;
                            break;
                        case "/":
                            arrTwo[0] = arrTwo[0] / arrTwo[1];
                            j = 1;
                            arrTwo[1] = 0;
                            break;
                        default:
                            j = 0;
                            break;
                    }
                }
                opr = char.ConvertFromUtf32(arrOne[i]);
        }
        Console.WriteLine("Result : " + arrTwo[0]);
        Console.ReadLine();

    }
}
}

String mathematical input and solution

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Solution 1

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