How do I create a custom error message with a try/catch block in C#?

Question

I'm doing a simple order total calculation function and I'm trying to figure out how to display a custom error message when the user input is the incorrect format. I.e. when they enter a non-integer in txtJava.Text, the message will display "Please enter an integer for Java"

    private void btnSubmit_Click(object sender, EventArgs e)
    {
        
        int Java;
        int Latte;
        int Mocha;
        int Frappe; 
        string Name = txtName.Text;
        double javaPrice = 1.25;
        double mochaPrice = 2.95;
        double lattePrice = 2.75;
        double frappePrice = 3.25;
        double dblTaxRate = .09;
        double dblSubtotal;
        double dblTax;
        double dblTotal;

        txtMessage.Text = "Thank you " + Name + " for your order!";
        
        Java = Convert.ToInt32(txtJava.Text);
        Latte = Convert.ToInt32(txtLatte.Text);
        Mocha = Convert.ToInt32(txtMocha.Text);
        Frappe = Convert.ToInt32(txtFrappe.Text);
        dblSubtotal = Java * javaPrice + Mocha * mochaPrice + Frappe * frappePrice + Latte * lattePrice;
        dblTax = dblSubtotal * dblTaxRate;
        dblTotal = dblSubtotal + dblTax;

        txtSubtotal.Text = dblSubtotal.ToString("C2");
        txtTax.Text = dblTax.ToString("C2");
        txtTotal.Text = dblTotal.ToString("C2");

Your title suggests there is a `try/catch` block to add a custom error to, but the posted code has no such block. — Scott Hunter, Apr 29 '22 at 14:49
You could just....add a `try/catch` and (im guessing) write a `txtMessage.Txt` in the catch — JamesS, Apr 29 '22 at 14:50
You seem to know somehow that you need a try/catch (you don't actually but might use it) for that then what have you tried with it? — Ralf, Apr 29 '22 at 14:51
You probably don't need a try/catch and instead want to TryParse the field and then set a label or something to an error. — nullforce, Apr 29 '22 at 14:54
1. Don't error out on the user. Make it impossible to enter invalid inputs, by using the appropriate input component. Which in your case (assuming winforms) would be a ["numeric updown"](https://learn.microsoft.com/en-us/dotnet/desktop/winforms/controls/numericupdown-control-windows-forms?view=netframeworkdesktop-4.8). (There is also one in WPF, I believe) 2. Do not use floating point types for monetary amounts. — Fildor, Apr 29 '22 at 15:46
Please provide enough code so others can better understand or reproduce the problem. — Community, Apr 29 '22 at 17:40
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score 2 · Answer 1 · edited Apr 29 '22 at 19:51

Avoid using try Prase or try catch in this scenario. It is better to change the textbox input type to be a number only.

I can't see what type of application you are running, but if its a webForms application you could alter the markup to look something like this:

<input type="number" id="quantity" name="quantity" min="1" max="100">

If its a WPF application: Allow only numeric entry in WPF Text Box

If this doesn't help you may need to provide more code. Give us a bit more context.

Happy coding.

score 0 · Answer 2 · answered Apr 29 '22 at 14:57

0

This code, instead of Java = Convert.ToInt32(txtJava.Text);

if (!TryParse(txtJava.Text, Java)) {
      //Display the text you want
}

In addition, your variables are not with the same naming convention ;)

answered Apr 29 '22 at 14:57

Dylan El Bar

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1
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How do I create a custom error message with a try/catch block in C#?

2 Answers2