Input string was not in the correct format when parsing integers

Question

I added a textbox to my form and I'm trying to get the text from it but it comes up with an exception saying

"Input string was not in the correct format."

This is my code:

deleteQuestion = Convert.ToInt32(textBox6.Text);
addQuestion = Convert.ToInt32(textBox7.Text);

listOfQuestions.RemoveAt(deleteQuestion - 1);

foreach (RichTextBox box in boxForQuestions)
{
       if (Convert.ToInt32(box.Tag) == deleteQuestion - 1)
       {
              boxForQuestions.Remove(box);
       }
}

In the second part of the code my intention is to delete dynamically added rich text box.

Answer 1

Use Int32.TryParse if you are not in control of what your user types in those textboxes

int deleteQuestion;
if(!Int32.TryParse(textBox6.Text, out deleteQuestion))
{
    MessageBox.Show("Not a valid number to delete a question!");
    return;
}
int addQuestion;
if(!Int32.TryParse(textBox7.Text, out addQuestion))
{
    MessageBox.Show("Not a valid number to add a question!");
    return;
}

Of course, the same should be considered for the Tag property used inside the loop but this is set by your code so I presume that it is safe to consider it a valid integer

Another problem in your code is the remove inside the foreach loop. This cannot be done, you cannot change a collection while iterating over it. If you really need to remove an element from that collection you should consider to use a normal for... loop and looping from the last element towards the first one