How can I add up four numbers from textboxes together and display the answer in a seperate textbox in visual studio?

Question

Visual Basics In my code I'am getting the user to enter the length and height of each of the four walls. I got the code to multiply the length by the height to work out the area of each wall and display each of the four areas in separate text boxes. Now I want to add up the four numbers that are in the text boxes and display the answer in a separate text box when I click a button.

This is the code that I have at the moment;

    Dim txtLength1 As Integer
    Dim txtLength2 As Integer
    Dim txtLength3 As Integer
    Dim txtLength4 As Integer
    Dim txtHeight1 As Integer
    Dim txtHeight2 As Integer
    Dim txtHeight3 As Integer
    Dim txtHeight4 As Integer
    Dim Area As Integer

    Area = TotalArea.Text

    txtLength1 = Length1.Text
    txtHeight1 = Height1.Text
    txtLength2 = Length2.Text
    txtHeight2 = Height2.Text
    txtLength3 = Length3.Text
    txtHeight3 = Height3.Text
    txtLength4 = Length4.Text
    txtHeight4 = Height4.Text


    Area1.Text = txtLength1 * txtHeight1
    Area2.Text = txtLength2 * txtHeight2
    Area3.Text = txtLength3 * txtHeight3
    Area4.Text = txtLength4 * txtHeight4

    Area = Area1.Text + Area1.Text + Area3.Text + Area4.Text

End Sub

End Class

When I run this code I get an error saying "Conversion from string "" to type 'Integer' is not valid."

Answer 1

Without taking into account peoples tendency to write other stuff than integers this would do the trick:

Dim txtLength1 As Integer
Dim txtLength2 As Integer
Dim txtLength3 As Integer
Dim txtLength4 As Integer
Dim txtHeight1 As Integer
Dim txtHeight2 As Integer
Dim txtHeight3 As Integer
Dim txtHeight4 As Integer
Dim Area As Integer

Area = Convert.ToInt32(TotalArea.Text)

txtLength1 = Convert.ToInt32(Length1.Text)
txtHeight1 = Convert.ToInt32(Height1.Text)
txtLength2 = Convert.ToInt32(Length2.Text)
txtHeight2 = Convert.ToInt32(Height2.Text)
txtLength3 = Convert.ToInt32(Length3.Text)
txtHeight3 = Convert.ToInt32(Height3.Text)
txtLength4 = Convert.ToInt32(Length4.Text)
txtHeight4 = Convert.ToInt32(Height4.Text)

Dim Area1Total As Integer = txtLength1 * txtHeight1
Dim Area2Total As Integer = txtLength2 * txtHeight2
Dim Area3Total As Integer = txtLength3 * txtHeight3
Dim Area4Total As Integer = txtLength4 * txtHeight4

Area1.Text = Area1Total
Area2.Text = Area2Total
Area3.Text = Area3Total
Area4.Text = Area4Total

Area = Area1Ttotal + Area2Total + Area3Total + Area4Total

Edit: Did some minor adjustments in order for you to be able to have the last Area part as it should aswell (since the .Text will make it into a string again).

Edit 2:

If the "TotalArea" Control is not a field that the user should fill in, but rather a sum of the total area as calculated from the various lengths and heights, your code should look like this:

Dim txtLength1 As Integer
Dim txtLength2 As Integer
Dim txtLength3 As Integer
Dim txtLength4 As Integer
Dim txtHeight1 As Integer
Dim txtHeight2 As Integer
Dim txtHeight3 As Integer
Dim txtHeight4 As Integer
Dim Area As Integer

txtLength1 = Convert.ToInt32(Length1.Text)
txtHeight1 = Convert.ToInt32(Height1.Text)
txtLength2 = Convert.ToInt32(Length2.Text)
txtHeight2 = Convert.ToInt32(Height2.Text)
txtLength3 = Convert.ToInt32(Length3.Text)
txtHeight3 = Convert.ToInt32(Height3.Text)
txtLength4 = Convert.ToInt32(Length4.Text)
txtHeight4 = Convert.ToInt32(Height4.Text)

Dim Area1Total As Integer = txtLength1 * txtHeight1
Dim Area2Total As Integer = txtLength2 * txtHeight2
Dim Area3Total As Integer = txtLength3 * txtHeight3
Dim Area4Total As Integer = txtLength4 * txtHeight4

Area1.Text = Area1Total
Area2.Text = Area2Total
Area3.Text = Area3Total
Area4.Text = Area4Total

Area = Area1Ttotal + Area2Total + Area3Total + Area4Total
TotalArea.Text = Area