VB.NET - Can't get Integer to work - vb.net

Question

I'm working with Windows Forms Application in Visual Studio 2015, using .NET Framework 4.5.2. So I'm making a simple program which includes a label to display a value. The label (called lblMoney) displays the currency (in this case, $) and then the value (e.g 350). Together it looks like $350.
Now, I made another form with a textbox called txtCash and a button called bApply. You enter any integer (e.g 350) into txtCash. When you press bApply, the number in txtCash will add to the number in lblMoney. So, if you had 5 in lblMoney, and you entered 350 in txtCash, lblMoney would display 355.
Here's my code to add to the number:
My.Forms.VeilSideCash.lblMoney.Text = cstrx + txtCash.Text.ToString
The form VeilSideCash is the form that holds lblMoney.
Here's the code for cstrx:
Dim cstrx = "$" & Val(My.Settings.Money.ToString)
The problem here is that, instead of overwriting to lblMoney, the new number is just added after the original number. So if lblMoney has 5 and you enter 350 into txtCash, lblMoney looks like $5350.
How would I go about overwriting with the new number (adding to) instead of replacing?
Any help would be appreciated. Feel free to edit incase I messed something up while explaining.

Answer 1

The problem with your code is the Option Strict setting for your project. You have it set to Off and this allows your code to freely treat strings as they were numbers and try to use them in mathematical operations.
But, when you use the + operator between two strings, it doesn't matter if, for a human being, the two strings represent a number, the compiler see them as strings (cstrx, txtCash.Text) and thinks that you want to use the concatenation operator defined for strings (the +). Yielding wrong (for you) results .
I really suggest you to not use the automatic conversions made by the compiler on your code, instead, when you need to do math operations, always convert your strings to numbers and do the math with variables of numeric type (You could also change the Option Strict to On, but you should be prepared to solve a lot of problems in your current code)
Instead, with a proper numeric approach, you get the text inside txtCash and try to check if your user has correctly typed a decimal value.
Dim cash As Decimal
if Not decimal.TryParse(txtCash.Text, cash) Then
MessageBox.Show("Invalid cash value")
Return
End if
Now get the text of lblMoney and convert it back to a decimal number alerting the compiler that there is a currency symbol in the text to convert
Dim current As Decimal
current = decimal.Parse(lblMoney.Text, NumberStyles.Currency, CultureInfo.CurrentCulture)
Now you have two numbers and the + operator does what you expect. It adds the two numbers together. Finally you could write back the result with a proper currency formatting
Dim result as Decimal
result = current + cash
lblMoney.Text = result.ToString("C")

Answer 2

You need to remove the "$" and convert to a number. I used a decimal so you can include cents if you want:
Dim sum As Decimal
sum = Val(cstrx.Replace("$","")) + Val(txtCash.Text)
My.Forms.VeilSideCash.lblMoney.Text = sum.ToString()
Dim cstrx = sum.ToString("C")
Note that I used the "C" to format the sum as currency. That automatically puts the $ on for you, or uses other currency symbols for other countries.
I'm not a big VB.net user, so my syntax may be slightly off.

Answer 3

When you use the + operator with string unexpected results can occur. In this case the string with a $ cannot be implicitly converted so you should explicit convert it
Once you convert your strings to a number type you can then use the + operator and they can be implicitly converted back to a string.
My.Forms.VeilSideCash.lblMoney.Text = decimal.Parse(cstrx, NumberStyles.Currency)
+ decimal.Parse(txtCash.Text ,NumberStyles.Currency)