This is a Sample calculator that I created in visual basic 2008, and this sample will be more useful for learners who are interested in VB 2008 and fortunately the VS 2019 can upgrade the source code perfectly. You can study it and modify it as more as you like.

How to Build a Simple Calculator

First, create an Interface for your calculator which has the following:

• TextField
  
• Buttons for the numbers
  
• Buttons for the Operators
  
• Button for the Result
  
• Off, Clear, and Backspace Button
  

In my Case, this is the interface I used.

After that, set the variables for the operator, value 1, value 2, and other needed for operations.

1. Option
   
   Explicit
   
   On
   
2. 
   
3. Public
   
   Class Form1
   
4. Dim
   
   Operand1 As
   
   Double
   
5. Dim
   
   Operand2 As
   
   Double
   
6. Dim
   
   [Operator] As
   
   String
   
7. 
   
8. Dim
   
   hasDecimal As
   
   Boolean
   
9. Dim
   
   tmpValue As
   
   Double
   
10. End
    
    Class
    

Then, for each number buttons. For script below, my textfield named as "txtInput" and "cmd1" for my number 1 button.

1. Private
   
   Sub
   
   cmd1_Click(ByVal
   
   sender As
   
   System.Object
   
   , ByVal
   
   e As
   
   System.EventArgs) Handles cmd1.Click
   
2. txtInput.Text = txtInput.Text & sender.text
   
3. End
   
   Sub
   

For the operation buttons except for the square root button, follow the script below and change the "[Operator]" value according to the operator you have set to the button.

1. Private
   
   Sub
   
   cmdAdd_Click(ByVal
   
   sender As
   
   System.Object
   
   , ByVal
   
   e As
   
   System.EventArgs) Handles cmdAdd.Click
   
2. Operand1 = Val(txtInput.Text)
   
3. txtInput.Text = ""
   
4. txtInput.Focus()
   
5. [Operator] = "+"
   
6. End
   
   Sub
   

And for the equal/result button. Use the following code below.

1. Private
   
   Sub
   
   Button23_Click(ByVal
   
   sender As
   
   System.Object
   
   , ByVal
   
   e As
   
   System.EventArgs) Handles Button23.Click
   
2. Dim
   
   Result As
   
   Double
   
3. Operand2 = Val(txtInput.Text)
   
4. 
   
5. Select
   
   Case
   
   [Operator]
   
6. Case
   
   "+"
   
7. Result = Operand1 + Operand2
   
8. txtInput.Text = Result.ToString()
   
9. Case
   
   "-"
   
10. Result = Operand1 - Operand2
    
11. txtInput.Text = Result.ToString()
    
12. Case
    
    "/"
    
13. Result = Operand1 / Operand2
    
14. txtInput.Text = Result.ToString()
    
15. Case
    
    "*"
    
16. Result = Operand1 * Operand2
    
17. txtInput.Text = Result.ToString()
    
18. Case
    
    "^"
    
19. Result = Operand1 ^ Operand2
    
20. txtInput.Text = Result.ToString()
    
21. Case
    
    "%"
    
22. Result = Operand1 * 1 / 100
    
23. txtInput.Text = Result.ToString()
    
24. 
    
25. 
    
26. End
    
    Select
    
27. 
    
28. txtInput.Text = Result.ToString()
    
29. 
    
30. End
    
    Sub
    

Next is we will create the function that calculates the square root of the value when the square root button will be clicked.

1. Private
   
   Sub
   
   cmdSqrtRoot_Click(ByVal
   
   sender As
   
   System.Object
   
   , ByVal
   
   e As
   
   System.EventArgs) Handles cmdSqrtRoot.Click
   
2. 'Make sure the input box has a value
   
3. If
   
   txtInput.Text.Length <> 0 Then
   
4. 'Assign our variable the value in the input box
   
5. tmpValue = CType(txtInput.Text, Double
   
   )
   
6. 'Perform the square root
   
7. tmpValue = System.Math.Sqrt(tmpValue)
   
8. 'Display the results in the input box
   
9. txtInput.Text = CType(tmpValue, String
   
   )
   
10. 'Clear the decimal flag
    
11. hasDecimal = False
    
12. End
    
    If
    
13. 
    
14. End
    
    Sub
    

And lastly, creating a function for the button clear, backspace, and decimal.

1. 'for the Decimal
   
2. Private
   
   Sub
   
   cmdDecimal_Click(ByVal
   
   sender As
   
   System.Object
   
   , ByVal
   
   e As
   
   System.EventArgs) Handles cmdDecimal.Click
   
3. If
   
   InStr(txtInput.Text, "."
   
   ) > 0 Then
   
4. Exit
   
   Sub
   
5. Else
   
6. txtInput.Text = txtInput.Text & "."
   
7. End
   
   If
   
8. End
   
   Sub
   
9. 
   
10. 'Clear Function
    
11. Private
    
    Sub
    
    CmdClearAll_Click(ByVal
    
    sender As
    
    System.Object
    
    , ByVal
    
    e As
    
    System.EventArgs) Handles CmdClearAll.Click
    
12. txtInput.Text = ""
    
13. 
    
14. End
    
    Sub
    
15. 
    
16. 'Off Function
    
17. Private
    
    Sub
    
    cmdOFF_Click(ByVal
    
    sender As
    
    System.Object
    
    , ByVal
    
    e As
    
    System.EventArgs) Handles CmdOff.Click
    
18. 
    
19. txtInput.Text = ""
    
20. 
    
21. End
    
    Sub
    

That's it, you can now try to debug your simple calculator and test if the Source Code works perfectly as planned. In case it doesn't work the way it should be, you download the working source code below.

Happy Coding : )

Note: Due to the size or complexity of this submission, the author has submitted it as a .zip file to shorten your download time. After downloading it, you will need a program like Winzip to decompress it.

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