Grade calculator C#
<p>i am quite new to c# and i am currently stuck..
Take a look at my program</p>

<pre><code>private void btn_calculate_Click(object sender, EventArgs e)
        {
            double[] credit = { 7.0, 6.0, 2.0 };
            String[] grade = { txt_IT.Text, txt_IFA.Text, txt_PPD .Text};
            double[] GPA = new double[3];
            bool blank = true;
            Double result = 0;

            for(int i = 0; i&lt;GPA.Length;i++)
            {
                if (grade[i] == "A" || grade[i] == "a")
                {
                    GPA[i] = 4.0;
                }
                if (grade[i] == "B" || grade[i] == "b")
                {
                    GPA[i] = 3.0;
                }
                if (grade[i] == "C" || grade[i] == "c")
                {
                    GPA[i] = 2.0;
                }
                if (grade[i] == "D" || grade[i] == "d")
                {
                    GPA[i] = 1.0;
                }
                if (grade[i] == "E" || grade[i] == "e")
                {
                    GPA[i] = 1.0;
                }
                if (grade[i] == "F" || grade[i] == "f")
                {
                    GPA[i] = 0.0;
                }
                if (grade[i] == "" &amp;&amp; blank)
                {
                    blank = false;
                    if (txt_IT.Text == "")
                    {
                        for (int print = 0; print &lt; GPA.Length; print++)
                        {
                            result += credit[print] / 8 * GPA[print];
                        }//for print
                        txt_result.Text = result.ToString("0.000");
                    }//nested if
                    if (txt_IFA.Text == "")
                    {
                        for (int print = 0; print &lt; GPA.Length; print++)
                        {
                            result += credit[print] / 9 * GPA[print];
                        }//for print
                        txt_result.Text = result.ToString("0.000");
                    }//nested if
                    if (txt_PPD.Text == "")
                    {
                        for (int print = 0; print &lt; GPA.Length; print++)
                        {
                            result += credit[print] / 13 * GPA[print];
                        }//for print
                        txt_result.Text = result.ToString("0.000");
                    }//nested if


                }//if

            }//for GPA
            for (int print = 0; print &lt; GPA.Length; print++)
            {
                result += credit[print] / 15 * GPA[print];
            }//for print
            if (blank == true)
            {
                txt_result.Text = result.ToString("0.000");
            }
        }

        private void btn_back_Click(object sender, EventArgs e)
        {
            Form1 data = new Form1();
            this.Hide();
            data.ShowDialog();
            this.Close();
        }
    }
}
</code></pre>

<p>This is somewhat correct, but my teacher wants it "special"
He wants a blank in it. </p>

<p>When i do it this way, the result is 0. Can anyone help?</p>

<p><img src="https://i.stack.imgur.com/OFsJ5.png" alt="enter image description here"></p>