Add values from two textboxes and display the sum in third textbox 3 but value of 1st aor 2nd textbox show in third textbox

Question

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Add values from two textboxes and display the sum in third textbox 3 but value of 1st aor 2nd textbox show in third textbox

Answer 1

TextBox3.Text = Convert.ToDouble(TextBox1.Text) + Convert.ToDouble(TextBox2.Text)

This will do it, just enter proper number. No exception handled.

To handle exception, use Double.TryParse instead of Convert.ToDouble .

Look at msdn example.

Answer 2

This will automatically change your value once you alter textbox1's value

private void textBox1_TextChanged(object sender, EventArgs e)
    {
        if (textBox1.Text.Length > 0 && textBox2.Text.Length > 0)
        {
            textBox3.Text = Convert.ToString(Convert.ToDouble(textBox1.Text) + Convert.ToDouble(textBox2.Text));
        }
        if (textBox1.Text.Length > 0 && textBox2.Text.Length == 0)
        {
            textBox3.Text = textBox1.Text;
        }
        if (textBox1.Text.Length == 0 && textBox2.Text.Length > 0)
        {
            textBox3.Text = textBox2.Text;
        }
        if(textBox1.Text.Length == 0 && textBox2.Text.Length == 0)
        {
            textBox3.Text = "0";
        }
    }

edit: treat textbox value as 0 when its empty.

This example will still error if you enter non-numeric values into the textbox.