Question

I want to obligate the person who is using my program to enter only numbers in the text label in c#. How can i do that?
example :
number of equations : (he should only enter a number)

This code to obligate him to enter a number between 2 and 10 but i need a code for letters

if (int.Parse(txt1.Text) < 2 || int.Parse(txt1.Text) > 10)
   {
     l6.ForeColor = System.Drawing.Color.Red;
     l6.Text = "Svp choisir un nombre entre 2 et 10 ... Soyez Logique!";
   }

Answer 1

if (txt1.Text.Trim().Length > 0)
{
    // Parse the value only once as it can be quite performance expensive.
    Int32 value = Int32.Parse(txt1.Text)

    if ((value >= 2) && (value <= 10))
    {
        l6.ForeColor = Color.Red;
        l6.Text = "Svp choisir un nombre entre 2 et 10 ... Soyez Logique!";

        // Clear the text...
        txt1.Text = "";
    }
    else
    {
        // Your code here...
    }
}

But, IMHO, TryParse is even better as it can handle bad string formats in a better way:

if (txt1.Text.Trim().Length > 0)
{
    Int32 value;

    if (!Int32.TryParse(txt1.Text, out value))
    {
        l6.ForeColor = Color.Red;
        l6.Text = "Svp choisir un nombre entre 2 et 10 ... Soyez Logique!";

        // Clear the text...
        txt1.Text = "";
    }
    else
    {
        // Your code here...
    }
}