Calculator in Visual Basic

[kxlemeiring]

Introduction:
This tutorial is on how to create a calculator in Visual Basic.

Design:
For this, we want the following;
A textbox named 'textbox1' to show the current output.
Four buttons for add, subtract, multiply and divide.
Ten buttons for the ten digits.
One button for the calculate process.

Variables:
Now we want to create some variable. First we create a curTotal integer which will hold the current total as an integer, and next we want a curAction which is also an integer but holds whether the next sum should be;
0 - Add
1 - Subtract
2 - Multiply
3 - Divide

Finally we also want a string variable named 'curValue' which will hold the current number to add/subtract/multiply or divide the curTotal to/from/by and a 'prevValue' to hold the one to append on to.

1. Dim
   
   curTotal As
   
   Integer
   
   = 0
   
2. Dim
   
   curValue As
   
   String
   
   = Nothing
   
3. Dim
   
   prevValue As
   
   String
   
   = Nothing
   
4. Dim
   
   curAction As
   
   Integer
   
   = -1
   

Note:
If you want your calculator to be more accurate, use double, float or long instead of integers.

Number Buttons:
Now for each of the number buttons click we want to add as a string the numeric value of the button to the end of the 'curValue' variable value. So for number 1 button we'll do 1, 2 is 2, 3 is 3, etc, etc...

1. Private
   
   Sub
   
   Button1_Click(sender As
   
   Object
   
   , e As
   
   EventArgs) Handles Button1.Click
   
2. curValue += "1"
   
3. End
   
   Sub
   
4. 
   
5. Private
   
   Sub
   
   Button2_Click(sender As
   
   Object
   
   , e As
   
   EventArgs) Handles Button2.Click
   
6. curValue += "2"
   
7. End
   
   Sub
   
8. 
   
9. Private
   
   Sub
   
   Button3_Click(sender As
   
   Object
   
   , e As
   
   EventArgs) Handles Button3.Click
   
10. curValue += "3"
    
11. End
    
    Sub
    
12. 
    
13. Private
    
    Sub
    
    Button4_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button4.Click
    
14. curValue += "4"
    
15. End
    
    Sub
    
16. 
    
17. Private
    
    Sub
    
    Button5_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button5.Click
    
18. curValue += "5"
    
19. End
    
    Sub
    
20. 
    
21. Private
    
    Sub
    
    Button6_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button6.Click
    
22. curValue += "6"
    
23. End
    
    Sub
    
24. 
    
25. Private
    
    Sub
    
    Button7_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button7.Click
    
26. curValue += "7"
    
27. End
    
    Sub
    
28. 
    
29. Private
    
    Sub
    
    Button8_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button8.Click
    
30. curValue += "8"
    
31. End
    
    Sub
    
32. 
    
33. Private
    
    Sub
    
    Button9_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button9.Click
    
34. curValue += "9"
    
35. End
    
    Sub
    
36. 
    
37. Private
    
    Sub
    
    Button10_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button10.Click
    
38. curValue += "0"
    
39. End
    
    Sub
    

Calculate Process:
Once the calculate button is clicked, this process will be ran. First we get the variable 'curValue's value (as a string), convert it to a 32 integer and then perform the appropriate action to the total ('curTotal'). Remember back to the beginning of the article where I mentioned the exact integer and action pairs of the 'curAction' variable...

1. Private
   
   Function
   
   calculate()
   
2. Dim
   
   toPerform As
   
   Integer
   
   = Convert.ToInt32(curValue)
   
3. If
   
   (curAction = 0) Then
   
4. 'add
   
5. Dim
   
   toPerform2 As
   
   Integer
   
   = toPerform + Convert.ToInt32(prevValue)
   
6. curTotal += toPerform2
   
7. ElseIf
   
   (curAction = 1) Then
   
8. 'sub
   
9. Dim
   
   toPerform2 As
   
   Integer
   
   = toPerform - Convert.ToInt32(prevValue)
   
10. curTotal -= toPerform2
    
11. ElseIf
    
    (curAction = 2) Then
    
12. 'mul
    
13. Dim
    
    toPerform2 As
    
    Integer
    
    = toPerform * Convert.ToInt32(prevValue)
    
14. curTotal *= toPerform2
    
15. ElseIf
    
    (curAction = 3) Then
    
16. 'div
    
17. Dim
    
    toPerform2 As
    
    Integer
    
    = toPerform / Convert.ToInt32(prevValue)
    
18. curTotal /= toPerform2
    
19. End
    
    If
    
20. curValue = Nothing
    
21. updateBox(curTotal.ToString())
    
22. End
    
    Function
    

As you can see, this function then runs another function named 'updateBox()' which will simply just set the text of the textbox to the string parsed to it...

1. Private
   
   Function
   
   updateBox(ByVal
   
   show As
   
   String
   
   )
   
2. TextBox1.Text = show
   
3. End
   
   Function
   

We can also do this for everytime the number buttons are clicked so the user can see the value of the variable 'curValue'...

1. Private
   
   Sub
   
   Button1_Click(sender As
   
   Object
   
   , e As
   
   EventArgs) Handles Button1.Click
   
2. curValue += "1"
   
3. updateBox(curValue)
   
4. End
   
   Sub
   
5. 
   
6. Private
   
   Sub
   
   Button2_Click(sender As
   
   Object
   
   , e As
   
   EventArgs) Handles Button2.Click
   
7. curValue += "2"
   
8. updateBox(curValue)
   
9. End
   
   Sub
   
10. 
    
11. Private
    
    Sub
    
    Button3_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button3.Click
    
12. curValue += "3"
    
13. updateBox(curValue)
    
14. End
    
    Sub
    
15. 
    
16. Private
    
    Sub
    
    Button4_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button4.Click
    
17. curValue += "4"
    
18. updateBox(curValue)
    
19. End
    
    Sub
    
20. 
    
21. Private
    
    Sub
    
    Button5_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button5.Click
    
22. curValue += "5"
    
23. updateBox(curValue)
    
24. End
    
    Sub
    
25. 
    
26. Private
    
    Sub
    
    Button6_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button6.Click
    
27. curValue += "6"
    
28. updateBox(curValue)
    
29. End
    
    Sub
    
30. 
    
31. Private
    
    Sub
    
    Button7_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button7.Click
    
32. curValue += "7"
    
33. updateBox(curValue)
    
34. End
    
    Sub
    
35. 
    
36. Private
    
    Sub
    
    Button8_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button8.Click
    
37. curValue += "8"
    
38. updateBox(curValue)
    
39. End
    
    Sub
    
40. 
    
41. Private
    
    Sub
    
    Button9_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button9.Click
    
42. curValue += "9"
    
43. updateBox(curValue)
    
44. End
    
    Sub
    
45. 
    
46. Private
    
    Sub
    
    Button10_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button10.Click
    
47. curValue += "0"
    
48. updateBox(curValue)
    
49. End
    
    Sub
    

Action Buttons:
Next we want to set the 'curAction' variables value to the relevant integer to which action button is clicked. 0=add, 1=subtract, 2=multiply, 3=divide. We also set prevValue to curValue and make curValue ready to accept a new input to perform the action with, followed by resetting the textbox using our previously created 'updateBox' function...

1. Private
   
   Sub
   
   Button11_Click(sender As
   
   Object
   
   , e As
   
   EventArgs) Handles Button11.Click
   
2. curAction = 0
   
3. prevValue = curValue
   
4. curValue = ""
   
5. updateBox(curValue)
   
6. End
   
   Sub
   
7. 
   
8. Private
   
   Sub
   
   Button12_Click(sender As
   
   Object
   
   , e As
   
   EventArgs) Handles Button12.Click
   
9. curAction = 1
   
10. prevValue = curValue
    
11. curValue = ""
    
12. updateBox(curValue)
    
13. End
    
    Sub
    
14. 
    
15. Private
    
    Sub
    
    Button13_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button13.Click
    
16. curAction = 2
    
17. prevValue = curValue
    
18. curValue = ""
    
19. updateBox(curValue)
    
20. End
    
    Sub
    
21. 
    
22. Private
    
    Sub
    
    Button14_Click(sender As
    
    Object
    
    , e As
    
    EventArgs) Handles Button14.Click
    
23. curAction = 3
    
24. prevValue = curValue
    
25. curValue = ""
    
26. updateBox(curValue)
    
27. End
    
    Sub
    

Calculate Button Press:
Finally we just need to run the calculate method on the calculate button mouse click event...

1. Private
   
   Sub
   
   Button15_Click(sender As
   
   Object
   
   , e As
   
   EventArgs) Handles Button15.Click
   
2. calculate()
   
3. End
   
   Sub