add numbers in textboxes

[HyperUniverse]

Hi

how do I add numbers from two different textboxes, and then show the result into one of them?

I tried this, but it won't work

Dim add_box As String
add_box = txt_box.Text
Dim derv_total As String
derv_total = txt_derv_total.Text

txt_derv_total.Text = derv_total + add_box

add_box is the box into which the user inputs a new number
txt_derv_total is the box that will hold the total accumulated.

thanks

[Shaggy Hiker]

Yeah, I'll bet you were a bit surprised by the result of that calculation.

Textboxes hold strings. You can't add strings, but the + operator is overloaded to perform concatenation on strings. What you were probably hoping would happen would be that the strings would magically turn into numbers and get added. Sometimes that happens, though the magic is an inefficient implicit conversion that you should be avoiding anyways. There are two solutions, either of which is ok:

1) Use either Integer.TryParse, Decimal.TryParse, or Double.TryParse to convert the string into a number and perform the calculation on the number. This is an explicit conversion, and .TryParse is the only safe way to convert user entered text. There are other, faster, easier, ways to convert a string to a number, but you have to be sure the string can be converted before you can use them, which is something you never know with user entered text. Look up .TryParse for examples. One or more examples are written every day on this forum, so I don't want to bother writing another. MSDN is another good source for an example.

2) Use NumericUpDown controls rather than textboxes. The NUD only allows numbers to be entered, and the .Value property returns the value as a Decimal, so you don't need to do any conversions.

[MetalInquisitor]

Maybe you should read about the very basics of VB.NET before starting coding anything.

http://homeandlearn.co.uk/NET/vbNet.html