button check

 private void submitbtnMath1_click(object sender, EventArgs e)
        {
            //submit button check if all answers are filled and save users anwers to answer lists
            //clear canvas and create new level
            submitBtnboolMath1 = true;
            String missingAnswer = "";
            for (int i = 0; i < countOfEquations; i++)
            {
                if (arrayTextBox[i, 4].Text == "")
                {
                    missingAnswer += (i + 1) + " ";
                }
                else
                {
                    //save answers from user
                }
            }
            if (missingAnswer != "")
            {
                MessageBox.Show("Nevyplnili jste " + missingAnswer);
            }
            else
            {
                //clear canvas after check all textboxes are filled
                taskGUIItems[EnumNumber.First].canvas.Children.Clear();
            }
        }