Break down a string in a regular interval

             Here i have given two ways .In which I am breaking down the string  when its index position is 10.


        string[] xx= new string[TextBox1.Text.Length];
        int l = xx.Length; int i;
        for (i = 0; i <= xx.Length - 1 && l>10; i += 10,l-=10)
        {
           st1 = TextBox1.Text.Substring(i,10 );
           st2 += st1+" ";
        }
        st1 = TextBox1.Text.Substring(i, l);
        st2 += st1 + " ";

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         int l = TextBox1.Text.Length; int i;
        for (i = 0; i <= TextBox1.Text.Length - 1 && l>10; i += 10,l-=10)
        {
           st2 += TextBox1.Text.Substring(i, 10) + " ";
        }
        st2 += TextBox1.Text.Substring(i, l) + " ";