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| Title | Build a calculator |
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| Keywords | calculator |
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| Categories | Utilities |
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The basic idea is to keep a stored value in the variable StoredValue. As the user clicks buttons, the program accumulates thge new value in the visible text box. When the user clicks an operator, the program remembers what operator it is. Then when the user clicks =, the program combines the stored value with the current;y displayed value using the operator.
The following code shows some of the key pieces. See the download for more details.
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' Add a number to the display.
Private Sub cmdNumber_Click(Index As Integer)
If NewEntry Then
txtDisplay.Text = Format$(Index)
NewEntry = False
Else
txtDisplay.Text = _
txtDisplay.Text & Format$(Index)
End If
End Sub
' Prepare to perform an operation.
Private Sub cmdOperator_Click(Index As Integer)
' Perform the previous operation.
cmdEquals_Click
' Remember this operation.
Operator = Index
' Start a new value.
NewEntry = True
End Sub
' Calculate the result of the previous operation.
Private Sub cmdEquals_Click()
Dim new_value As Double
If txtDisplay.Text = "" Then
new_value = 0
Else
new_value = CDbl(txtDisplay.Text)
End If
Select Case Operator
Case opNone
StoredValue = new_value
Case opAdd
StoredValue = StoredValue + new_value
Case opSubtract
StoredValue = StoredValue - new_value
Case opMultiply
StoredValue = StoredValue * new_value
Case opDivide
StoredValue = StoredValue / new_value
End Select
Operator = opNone
NewEntry = True
txtDisplay.Text = Format$(StoredValue)
End Sub
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This is a fairly complex application so I have not finished it completely. In particular, I have not thoroughly tested it and you could add other features like parentheses, square roots, expenents, scientific notation, trigonometric functions, etc.
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