BC30451 VisualBasic错误

Question

I'm trying to make a calculator in VisualBasic, however it throws this error at me. Replacing CastNumbers() with the functions' code fixes the error somewhat, but I'm still curious how to fix this. I couldn't find any relevant answers which I would understand on the internet, because this is my first programming project in 2 years (I started doing some stuff in CSharp , but I stopped).

Public Class Form1

    Private Sub b_ClickMe_Click(sender As Object, e As EventArgs) Handles b_ClickMe.Click
        MyTextBox.Text = "Hello"
        '---Dim firstNum As Integer = CInt(number1.Text)
        '---Dim secondNum As Integer = CInt(number2.Text)
        '---sum.Text = firstNum + secondNum
    End Sub

    Public Function CastNumbers()
    '//--- Converts input to integer, casts as firstNum and secondNum
        Dim firstNum As Integer = CInt(number1.Text)
        Dim secondNum As Integer = CInt(number2.Text)
    End Function

    Private Sub b_plus_Click(sender As Object, e As EventArgs) Handles b_plus.Click
        CastNumbers()
        sum.Text = firstNum + secondNum
    End Sub

    Private Sub b_minus_Click(sender As Object, e As EventArgs) Handles b_minus.Click
        CastNumbers()
        sum.Text = firstNum - secondNum
    End Sub

    Private Sub b_multiply_Click(sender As Object, e As EventArgs) Handles b_multiply.Click
        CastNumbers()
        sum.Text = firstNum * secondNum
    End Sub

    Private Sub b_divide_Click(sender As Object, e As EventArgs) Handles b_divide.Click
        CastNumbers()
        sum.Text = firstNum / secondNum
    End Sub

End Class

Answer 1

You have defined your variables in a function and trying to use them outside of that function. That is the problem.

Try this,

Public Class Form1
         Dim firstNum As Integer
         Dim secondNum As Integer
    Private Sub b_ClickMe_Click(sender As Object, e As EventArgs) Handles b_ClickMe.Click

        MyTextBox.Text = "Hello"

        'Dim firstNum As Integer = CInt(number1.Text)

        'Dim secondNum As Integer = CInt(number2.Text)

        'sum.Text = firstNum + secondNum

    End Sub

    Public Function CastNumbers() 'Converts input to integer, casts as firstNum and secondNum

        firstNum = CInt(number1.Text)

        secondNum = CInt(number2.Text)

    End Function

    Private Sub b_plus_Click(sender As Object, e As EventArgs) Handles b_plus.Click

        CastNumbers()

        sum.Text = firstNum + secondNum

    End Sub

    Private Sub b_minus_Click(sender As Object, e As EventArgs) Handles b_minus.Click

        CastNumbers()

        sum.Text = firstNum - secondNum

    End Sub

    Private Sub b_multiply_Click(sender As Object, e As EventArgs) Handles b_multiply.Click

        CastNumbers()

        sum.Text = firstNum * secondNum

    End Sub

    Private Sub b_divide_Click(sender As Object, e As EventArgs) Handles b_divide.Click

        CastNumbers()

        sum.Text = firstNum / secondNum

    End Sub

End Class

Answer 2

Thank you all for your help. The code now looks like this.

Public Class Form1

    Dim firstNum As Integer

    Dim secondNum As Integer

    Private Sub b_ClickMe_Click(sender As Object, e As EventArgs) Handles b_ClickMe.Click

        MyTextBox.Text = "Hello"

    End Sub

    Public Function ReadNumbers() 'Converts input to integer, casts as firstNum and secondNum

        firstNum = CInt(number1.Text)

        secondNum = CInt(number2.Text)

    End Function

    Private Sub b_plus_Click(sender As Object, e As EventArgs) Handles b_plus.Click

        ReadNumbers()

        sum.Text = firstNum + secondNum

    End Sub

    Private Sub b_minus_Click(sender As Object, e As EventArgs) Handles b_minus.Click

        ReadNumbers()

        sum.Text = firstNum - secondNum

    End Sub

    Private Sub b_multiply_Click(sender As Object, e As EventArgs) Handles b_multiply.Click

        ReadNumbers()

        sum.Text = firstNum * secondNum

    End Sub

    Private Sub b_divide_Click(sender As Object, e As EventArgs) Handles b_divide.Click

        ReadNumbers()

        sum.Text = firstNum / secondNum

    End Sub

End Class