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Visual Basic : Build a SIMPLE calculator

Discussion in 'Programming & Webmastering' started by Dark_Webster, Aug 14, 2008.

  1. Dark_Webster New Member

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    Hey all. I thought that this section needed a little help so there it is.
    For someone that wants to start programming in Visual Basic, I have a simple program that I'm going to show you.
    I will teach, step-by-step how to build a simple calculator.

    So here it goes ok?

    First, make sure you have at least Visual Studio 2005 (it's the best I've ever experimented and you will learn fast).

    [​IMG]

    Click the New Project button.
    To begin with, you need to create a Visual Basic application with an empty project, like shown on this image.
    The name of the project is at your criteria.

    [​IMG]

    Then, when the project is created, you should click with the right mouse button on the bold letters on the Solution Explorer,I mean the name of the project. Then go to Add, Windows Form. Now, it should appear the same window that appears on the image. Then again, the name of the form is at your criteria.

    [​IMG]

    Then double-click on the form you have just created and your window should look like this. If the toolbox doesn't appear, then go to View,Toolbox or press Ctrl+Alt+X.

    [​IMG]

    Then in the toolbox, look for Textbox. Click on it and draw two textboxes on the form. Again, the size is at your will.
    I will not change the name of the objects to keep things simple. Then look for label and draw one.
    Now click on the label you've just created. In the block Properties just below Solution Explorer, change AutoSize to False and clear the Label1 text in Text. Then it should be like on the image, except for position and size of objects.

    Now go to the toolbox and look for Button. Draw the first one, go to properties and in the Text value write Add.
    Draw the second one and in Text value write Subtract, draw the third and in Text value write Multiply. Finally, draw the fourth and in Texh value write Divide. Oh I forgot, after doing all that, click on the label that you've introduced on the form and look in Properties for BorderStyle. Change it to Fixed3D.

    Now that we have it all, we can now start to write the source code.

    [​IMG]

    Now, double-click on the Add button. It should appear a window like this. This window is the coder part of the program.
    It's where you write the source code of the program, more precisly, the Add button you've created on the form. Warning: Do not confuse Button1_Click with the Add button. Button1 is the name of the object to the program, Add is just a string to know what the button does.

    Then put this on the code:
    Code:
    Label1.Text = Val(TextBox1) + Val(TextBox2)
    This will add the value on Textbox1 with Textbox2 and show it on Label1. Now click on the design tab and double click on the subtract button and put the same code, you only need to change the signal to minus. Do the same procedure to Multiply and change it to the right signal. Now go click on the Divide button.

    This is the one that needs a different code, because it's more suspectible to errors like dividing 0 by 0.
    Put this code:
    Code:
            
            Try
                Label1.Text = Val(TextBox1.Text) / Val(TextBox2.Text)
            Catch ex As Exception
    
            End Try
    
    This will end the errors on dividing zero by zero or dividing without anything on the textboxes.

    [​IMG]

    The code should be like this (depending how are your tastes at formatting text).
    Ignore the warnings, the program still works perfectly. If you have followed all the steps, now try out the program.
    Click on the green play and try it :) .


    I know that this may look too easy, but I wanted to show to people that programming is not so boring. I hope you like it and if someone has corrections do do, please step foward.
    Last edited: Aug 14, 2008
    Oliver_FF says thanks.
  2. DanTheBanjoman Señor Moderator

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    What's the point of val()?
  3. SathyaBhat New Member

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    well the text box holds the values in string format, val() does type conversion from string to integer (number) so that the math operations can be done properly.
  4. DanTheBanjoman Señor Moderator

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    Val() doesn't convert to string, it takes a number from a string. You can still enter all kinds of pointless things in the box. Use an input mask and the whole issue is solved.
  5. Oliver_FF

    Oliver_FF New Member

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    SathyaBhat is correct, val(String) will type conversion from string to integer. It's vital because without it, the + will be String concatenation and 3 + 4 will suddenly result in 34.

    Dan is also correct that you can still enter all kinds of non-integers into the box. I suspect that val() with throw an exception if you do this - just catch it and set like "Math Error" as the result or something...

    Oh, and good effort Dark_Webster :) Some suggestions for some fun other related stuff:
    1. Factorise quadratic equations... 3x^2 + 2x +6 = 0
    2. Solve simultaneous equations 3x + 4y = 7, x + y = 2
  6. SathyaBhat New Member

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    Correct. but it seems it picks up the numbers only if the string starts with a number. If the string is like test123 then val() returns 0

    If the string is 123test231 then val() returns only 123.
  7. Oliver_FF

    Oliver_FF New Member

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    I'm suprised that it even returns anything, maybe i'm just too used to C/C++/C#/Java where it's mainly up to the programmer to make sure everything is used perfectly...
  8. chron New Member

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    in the textbox's keypress method insert:

    If e.KeyChar <> vbBack Then
    e.Handled = IIf(IsNumeric(e.KeyChar), False, True)
    End If

    This will take away the user's ability to insert anything other than numbers. If you're concerned about pasting info in using the right click menu, you can always insert a blank context menu and set the textbox's context menu property to point to the empty context menu.

    Using Val() is good because it's simple, but you can also declare an integer variable and set it using a convert.to function. For instance:

    dim x as integer = convert.toInt64(textbox1.text)

    then of course instead of using textbox1.text in your coding, you can just point to x

    happy coding
  9. DanTheBanjoman Señor Moderator

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    Why write code when you can simply use an input mask? Only allow numeric input and all is solved.
  10. chron New Member

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    I mean, either way is cool I guess lol. I normally use masked textboxes for things like phone number, zip, date, and ssn's. I suppose it depends on how many decimal places you want your calculator to be capable of...
  11. DanTheBanjoman Señor Moderator

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    Good point, decimals can change things.

    I guess my SQL teacher wasted my way of thinking. He used to bitch about me solving things frontend that could be done on the backend. And he always said anything that can be solved in the backend should be solved there. Which actually is true in most cases.
  12. DanTheBanjoman Señor Moderator

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    Perhaps something fun, how about we all make our own calculator in our fav language and publish the source for eachother to learn? I guess I can construct something tomorrow.
    It might draw some interest of people eager to learn but not knowing where to start. With that in mind I would say comments in code will be a requirement.
  13. DanTheBanjoman Señor Moderator

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  14. Dark_Webster New Member

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    Oh just one thing.

    When using masked textboxes, how can I make the cursor appear on the very left of it when I click on it? Because if I click on the middle of the textbox, it will start on the place that I clicked:).
  15. Dark_Webster New Member

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    And, I need to know also how to show a messagebox when an exception is catched...
  16. DanTheBanjoman Señor Moderator

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    There should be a property to align text.

    Use try/catch you can catch exceptions, just type "try" and vs will add the rest for you. It'll explain itself. Use msgbox("Omg the world exploded") to show a messagebox.
  17. Dark_Webster New Member

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    Try
    Sinal.Text = "/"
    BarraProgresso.Value = 0
    Resultado.Text = Val(Valor1.Text) / Val(Valor2.Text)
    BarraProgresso.Value = 100
    StatusCalculadora.Text = ("You've just divided something...")
    Catch ex As Exception
    MsgBox("You're smart xD")
    End Try

    Is the messagebox in the right place?

    If it is, when I do an exception it doesn't appear
  18. DanTheBanjoman Señor Moderator

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    But if you remove try/catch it does crash?
  19. Dark_Webster New Member

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    It does not... it only crashes if i divide with the textboxes empty... and try removes that error, but I wanted to show that messagebox when a exception ocurrs.
  20. DanTheBanjoman Señor Moderator

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    And it doesn't show the textbox when you leave the divide textbox empty?
  21. Dark_Webster New Member

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    No, it does not.
  22. DanTheBanjoman Señor Moderator

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    Look in my sample, it has some try/catch in it. See if there is anything different.
  23. Dark_Webster New Member

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    No it is the same, except the cases xD.

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