Question

I am getting error int pocet = int.Parse(textBox1.Text);

It says that data have some bad format, but I am writing only natural numbers to TextBox1

Answer 1

I suspect you’ve either got an empty string there, there’s whitespace at the start or end, or you’re writing in the thousands separators.

You can instruct the Int32.Parse method to handle some of those cases like this:

Int32.Parse(
   "  -12,340  ",
   NumberStyles.AllowLeadingWhite |
   NumberStyles.AllowThousands |
   NumberStyles.AllowTrailingWhite |
   NumberStyles.AllowLeadingSign,
   CultureInfo.CurrentCulture));

Note the current culture bit at the end is important because the thousands separator will be different depending on the culture the user has their computer set to.

This still won’t handle an empty string though – just check to see if the string is empty before doing the parsing.