I used Visual Studio to create an application that features 3 fields where 3 numbers can be added together. Now, I need to validate all 3 fields so that negative numbers cannot be added. If a negative number is entered, each field has also to return a unique message like: "please enter a positive first number."

I figured out how to do that for one field, but how do I set it up for all 3 fields to not accept negative numbers (and display a unique message)?

Here is what I have:

```
{
    int num = int.Parse(txtNum1.Text);

    if (num <0)
    {
        MessageBox.Show("Please enter a positive first number");
    }
    else
    {
        int num1 = int.Parse(txtNum1.Text);
        int num2 = int.Parse(txtNum2.Text);
        int num3 = int.Parse(txtNum3.Text);
        int sum = num1 + num2 + num3;
        txtResult.Text = sum.ToString();
    }

```

Hopefully this makes sense.