How to add or subtract a digit in the Textbox via a button?

Question

I want to add to a number in a TextBox generating a digit when the user clicks the " + " button and subtracts when he clicks the " - ". For example: the random number was 2. If I click on +, 3 appears. If I click on -, 1 appears.

From the looks of it, you can’t do addition and subtraction operations with TextBoxes, as in this code here, which was presented the CS00019 error:

private void btn_plus_Click(object sender, EventArgs e)
{ 
resultado.Text = resultado + 1;
}

Where the resultado.Text is the number converted into string and resultado the name of my TextBox.

How could I make it work?

Answer 1

Use the TryParse() if you do not want to generate an error if the value is invalid. You can treat as you wish if it is invalid. In this case I ignored the sum.

private void btn_plus_Click(object sender, EventArgs e) {
    int numero;
    if (int.TryParse(resultado.Text, out numero)) {
        resultado.Text = (numero + 1).ToString();
    }
}

Behold working in the ideone. And in the .NET Fiddle. Also put on the Github for future reference. I had to adapt since I’m not in a Winforms application.

Just use the Parse() (difference) whenever he manages an exception if he can’t parse the number, which is not common to want this. It is better to know that it was wrong and treat right there without the cost of the exception, even more that most programmers treat exceptions wrongly.

Answer 2

C# is not like PHP that performs operations with what lies ahead, it needs to work with certain types, and as you yourself expressed the value of the Textbox field is text (or string). To work with mathematical operations you first need to convert the value to some numeric type like Int, Float and etc...

Then your code would be...:

Para Somar:

resultado.Text = (int.Parse(resultado.Text) + 1).ToString();

Or to Subtract:

resultado.Text = (int.Parse(resultado.Text) - 1).ToString();

Answer 3

private void btn_plus_Click(object sender, EventArgs e)
{ 
    int boxI = resultado.Text        
    resultado.Text = boxI + 1;
}

I haven’t had time to test it, but it should work.