C# Calculator Class

Question

I was given this homework assignment, which I have been having a hard time with. The form was written and we had to write the class. Currently when I run the program my equals button does not appear to be working. I'm unsure why and I was wondering if someone could help me understand what I am missing. I believe I have written my class correctly. In my head what is going on is the calculator is calling the "currentValue" so I am constantly updating with the method I am using in my operators.

Am I in the right direction?

And why isn't my equals button calling the current value. The last time I ran this, if I typed 9 + 3 + then my display would populate with 12 and wait for me to enter the next number. So in theory why wouldn't my equals button load the answer? I believe I am calling the correct item yet I keep getting my initial entry. For instance if I typed 9 + 9 and hit = I keep getting 9.

Here is the calculator code (the part provided):

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace Calculator
{
public partial class frmCalculator : Form
{
    public frmCalculator()
    {
        InitializeComponent();
    }

    // The following fields are used to store the value that's currently
    // displayed by the calculator. displayString is a string value that's
    // constructed as the user clicks numeric keys and the decimal and +/-
    // key. The Convert.ToDecimal method is then used to convert this to a decimal
    // field that's stored in displayValue.
    private string displayString;
    private decimal displayValue;

    // The following bool fields are used to control numeric entry.
    // newValue indicates whether the calculator is ready to receive a
    // new numeric value. Once the user clicks a digit button, newValue is
    // set to false. When the user clicks a button that "enters" the value, 
    // such as Add or Equals, newValue is set to true so the user can enter 
    // another value.
    // decimalEntered is used to restrict the entry to a single decimal point.
    // It is set to true whenever newValue is set to true, and it is set to 
    // false whenever the user clicks the decimal point button.
    private bool newValue;
    private bool decimalEntered;

    private Calculator calc = new Calculator();

    private void Form1_Load(object sender, System.EventArgs e)
    {
        displayValue = 0;
        displayString = displayValue.ToString();
        newValue = true;
        decimalEntered = false;
    }

    // This method handles the 0 through 9 keys, appending the digit clicked
    // to the displayString field. 
    private void btnNumber_Click(object sender, System.EventArgs e)
    {
        if (newValue)
        {
            displayString = "";
            newValue = false;
        }
        displayString += ((Button)sender).Tag.ToString();
        displayValue = Convert.ToDecimal(displayString);
        txtDisplay.Text = displayValue.ToString();
    }

    // This method removes the last character from the displayString field.
    private void btnBackSpace_Click(object sender, System.EventArgs e)
    {
        if (displayString.Length > 1)
        {
            displayString = displayString.Substring(0, displayString.Length - 1);
            displayValue = Convert.ToDecimal(displayString);
            txtDisplay.Text = displayValue.ToString();
        }
        else
        {
            displayString = "";
            displayValue = 0;
            txtDisplay.Text = displayValue.ToString();
        }

    }

    private void btnClear_Click(object sender, System.EventArgs e)
    {
        calc.Clear();
        displayString = "";
        displayValue = 0;
        txtDisplay.Text = displayValue.ToString();
        newValue = true;
        decimalEntered = false;
    }

    // This method appends a decimal point to the displayString field if the
    // user has not already entered a decimal point.
    private void btnDecimal_Click(object sender, System.EventArgs e)
    {
        if (newValue)
        {
            displayString = "0";
            newValue = false;
        }
        if (!decimalEntered)
        {
            displayString += ".";
            displayValue = Convert.ToDecimal(displayString);
            txtDisplay.Text = displayValue.ToString();
            decimalEntered = true;
        }
    }

    private void btnSign_Click(object sender, System.EventArgs e)
    {
        displayValue = -displayValue;
        txtDisplay.Text = displayValue.ToString();
    }

    private void btnAdd_Click(object sender, System.EventArgs e)
    {
        calc.Add(displayValue);
        newValue = true;
        decimalEntered = false;
        displayValue = calc.CurrentValue;
        txtDisplay.Text = displayValue.ToString();
    }

    private void btnSubtract_Click(object sender, System.EventArgs e)
    {
        calc.Subtract(displayValue);
        newValue = true;
        decimalEntered = false;
        displayValue = calc.CurrentValue;
        txtDisplay.Text = displayValue.ToString();
    }

    private void btnMultiply_Click(object sender, System.EventArgs e)
    {
        calc.Multiply(displayValue);
        newValue = true;
        decimalEntered = false;
        displayValue = calc.CurrentValue;
        txtDisplay.Text = displayValue.ToString();
    }

    private void btnDivide_Click(object sender, System.EventArgs e)
    {
        calc.Divide(displayValue);
        newValue = true;
        decimalEntered = false;
        displayValue = calc.CurrentValue;
        txtDisplay.Text = displayValue.ToString();
    }

    private void btnSqrt_Click(object sender, System.EventArgs e)
    {
        calc.SquareRoot(displayValue);
        displayValue = calc.CurrentValue;
        txtDisplay.Text = displayValue.ToString();
    }

    private void btnReciprocal_Click(object sender, System.EventArgs e)
    {
        try
        {
            calc.Reciprocal(displayValue);
            displayValue = calc.CurrentValue;
            txtDisplay.Text = displayValue.ToString();
        }
        catch (DivideByZeroException)
        {
            displayValue = 0;
            txtDisplay.Text = "Cannot divide by zero.";
            newValue = true;
            decimalEntered = false;
        }
    }

    private void btnEquals_Click(object sender, System.EventArgs e)
    {
        try
        {
            if (newValue)
                calc.Equals();
            else
                calc.Equals(displayValue);
            displayValue = calc.CurrentValue;
            txtDisplay.Text = displayValue.ToString();
            newValue = true;
            decimalEntered = false;
        }
        catch (DivideByZeroException)
        {
            displayValue = 0;
            txtDisplay.Text = "Cannot divide by zero.";
            newValue = true;
            decimalEntered = false;
        }
    }

}

}

Here is my class (The part I wrote):

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

namespace Calculator
{
public class Calculator
{

    public Decimal displayValue;
    public Decimal currentValue;

     public void Add(Decimal displayValue)
    {

        currentValue += displayValue;

    }

     public void Subtract(Decimal displayValue)
     {
         currentValue -= displayValue;
     }

     public void Multiply(Decimal displayValue)
     {
         currentValue *= displayValue;
     }


     public void Divide(Decimal displayValue)
     {
         currentValue /= displayValue;
     }

     public void SquareRoot(Decimal displayValue)
     {
         currentValue = (decimal)Math.Sqrt(Convert.ToDouble(displayValue));
     }

     public void Reciprocal(Decimal displayValue)
     {
         currentValue = 1 / displayValue;
     }

     public decimal Equals()
     {
         return currentValue;
     }


     public void Clear()
     {
         currentValue = 0;
         displayValue = 0;
     }

     public decimal CurrentValue
     {
       get
          {
           return currentValue;
          }

     }
}

}

Answer 1

In the main code, you have called the Equal() method like this:

if (newValue)
    calc.Equals();
else
    calc.Equals(displayValue); //Your class do not have this.

So, you should do this first

//I am not sure why you need to pass in the displayValue parameter, so I presume it would not return anything.
public void Equal(Decimal displayValue)
{
        //Do the things you suppose to do
}

And for your 9 + 9 = 9 problem, it is simply because in your code, you only press your click event Add_Button for once. Make a break point at your Add() method. Then try to do like this:

9 --> press your Add_Button --> 9 --> press your Add_Button --> check your currentValue

Answer 2

displayValue is both a class field and a method argument. Is that your intention? You need to make this.displayValue = ... when you assign to the field argument in order to make it clear what you are doing. Currently you are overwriting the local copy of the argument and the field value is always 0.

Just delete the decimal displayValue; declaration (and from the Clear() function) and then store the displayValue outside of the class in the form.

public class Calculator
{

    //public Decimal displayValue;
    public Decimal currentValue;

    public void Add(Decimal displayValue)
    {

        currentValue+=displayValue;

    }
    ...
    public void Clear()
    {
        currentValue=0;
        //displayValue=0;
    }

    public decimal CurrentValue
    {
        get { return currentValue; }

    }
}

class Program
{
    static void Main(string[] args)
    {
        Calculator calc=new Calculator();
        calc.Add(1000m);
        calc.Divide(25m);
        calc.Subtract(8m);

        Console.WriteLine(calc.CurrentValue);
        // (1000/25)-8 = 32
    }
}

Answer 3

The main problem I see with your code is that you are only adding one of your operands, So for example 8 + 8 will always equal 8 for example.You have to do something like this ( included Add and reciprocal functions only):

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

namespace Calculator
{
public class Calculator
{

    public Decimal displayValue;
    public Decimal currentValue;

    private Decimal Operand_1;
    private Decimal Operand_2;

    private bool Operand_1_Added = false;
    private bool Operand_2_Added = false;

    private string Operation = "";

   private void AddOperand(Decimal Operand)
    {
            if(Operand_1_Added) 
                {
                  Operand_2 = Operand;
                  Operand_2_Added = true;
                }
            else {
                  Operand_1 = Operand;
                  Operand_1_Added = true;
                  currentValue = Operand_1;
                 }
     }



   public void Add(Decimal Arg1)
    {  
        this.AddOperand(Arg1);
        Operation = "Addition";
    }

   public void Reciprocal(Decimal Arg)
    {
     this.AddOperand(Arg);
     Operation = "Reciprocal";
    }


     public void Clear()
     {
         currentValue = 0;
         displayValue = 0;
         Operand_1 = 0;
         Operand_2 = 0;
     }

     public void Equals()
      {
         switch(Operation)
             {
                 case "Addition": 
                          currentValue = Operand_1 + Operand_2;
                          break;
                 case "Reciprocal":
                          currentValue = 1/Operand_1;
                          break;
                 default: break; 
              }
      }

   public void Equal(Decimal displayValue)
   {
    currentValue = displayValue;
   }
     public decimal CurrentValue
     {
       get
          {
           return currentValue;
          }

     }
}

Haven't tested code but this should work with the form class.

Answer 4

Let's look at the requirement:

"The results of multipication should show no more decimal places than the result of the first number than in the second number. Example 55.5*89.68 = 4977.240"

The natural of multiplication in basic arithmetic means that this happens by default anyway. Eg. you're never going to multiply XX by X.XX and get result X.XXXXXXX... - it just can't happen.

Formatting is therefore easy - if you need to explicitly format then format as num.ToString("#.##############") which allows for a while bunch of numbers.

You haven't outlined any requirements for Division, so I can't comment.

BTW - if you say x = 1 / 3 and y = z * x, then you are going to get a lot of numbers after the decimal place, because x is .333333333... to start with. This is within the requirement AFAICT.