How to write simple ErrorMessage function

Question

I'm trying to understand, how to write simple error message function, which would react if string was entered in text-boxes instead of numbers.

Let's say i want to calculate value 1 and value 2, but display error in label if string was entered.

EXAMPLE

1 + 1 = 2

a + 1 = error

My code

Calculate.cs

public static string ErrorMessage()
    {
        string msg = "";
        try
        {
            //do sth
        }
        catch (Exception ex)
        {
            msg = "Wrong value";
        }
        return msg;
    }

Calculator.asxc

protected void Button1_Click(object sender, EventArgs e)
    {
    try
        {

            //calculate - works
        }
    catch
        {
             Error.Text = Calculate.ErrorMsg();
        }

Also tried sth like this, but doesn't seem to be working:

Calculate.cs

public static bool ErrorMessage(string value1, string value2)
    {
        bool check = true;
        string error;
        if (value1 != "" && value2 != "")
        {
            check = true;
        }
        if (value1 =="" || value2 =="")
        {
            check = false;
            error = "Error!";
        }
        return check;    
    }

Calculator.asxc

protected void Button1_Click(object sender, EventArgs e)
    {
    try
        {

            //calculate - works
        }
        //
        catch
        {
        bool res = false;

            res = Calculate.ErrorMessage(textBox1.Text, textBox2.Text);

            Error.Text = res.ToString();
        }

I know that the second method doesn't check for numeric numbers, but i was just trying to implement some logic and see if ti works..but nothing does

I'm lost...please help

Answer 1

As I understand, you work with numbers ad want your application to display error message if user enters a string instead of number.

You should use Int32.Parse() or Int32.TryParse() methods. More info about Parse and TryParse here.

Method TryParse is good enough as it doesn`t throw an error if it cannot parse string into integer, it returns false instead.

Here is example how to use this method in your classes, change Button1_Click method something like this:

protected void Button1_Click(object sender, EventArgs e)
{
    int a;
    int b;

    // Here we check if values are ok
    if(Int32.TryParse(textBox1.Text, out a) && Int32.TryParse(textBox2.Text, b))
    {
        // Calculate works with A and B variables
        // don't know whats here as you written (//calculate - works) only
    }
    // If the values of textBoxes are wrong display error message
    else
    {
        Error.Text = "Error parsing value! Wrong values!";
    }
}

If you need to use ErrorMessage method, then here it is how you can change your ErrorMessage method, but this is more complex, the first example is easier:

public static string ErrorMessage(string value1, string value2)
{
    int a;
    int b;

    // If we have an error parsing (note the '!')
    if(!Int32.TryParse(value1, out a) || !Int32.TryParse(value2, b))
    {
        return "Error parsing value! Wrong values!";
    }

    // If everything is ok
    return null;
}

Hope this helps, ask if you need more info.