C# Exception thrown: 'System.FormatException' in mscorlib.dll

Question

Exception thrown: System.FormatException in mscorlib.dll

{"Input string was not in a correct format."}

I have been at this all day. Please help! Those above were the error messages btw. I am a bit new to C# so I could use a bit more detailed answers (I don't get the jargon so well)

public partial class Form1 : Form
{
    double a, b, d, f, g, t;
    string z;
    int c;
    public Form1()
    {
        InitializeComponent();
    }
    private void Form1_Load(object sender, System.EventArgs e)
    {
    }
    private void button7_Click(object sender, EventArgs e)
    {
        a = Convert.ToDouble(textBox18.Text);
        z = Convert.ToString(comboBox1);
        d = Convert.ToDouble(checkBox1);
        f = Convert.ToDouble(textBox13.Text);
        g = Convert.ToDouble(textBox14.Text);
        t = Convert.ToDouble(textBox19.Text);
        if (z == "a")
        {
            textBox15.Text = Convert.ToString(a * g * d * t);
        }
        else if (z == "b")
        {
            textBox15.Text = Convert.ToString(c);
        }
    }

Solution

These could be the possible issues,

the given input may not be in those format which can be converted to double

a = Convert.ToDouble(textBox18.Text);
    z = Convert.ToString(comboBox1.SelectedValue);
    d = Convert.ToDouble(checkBox1.Checked);
    f = Convert.ToDouble(textBox13.Text);
    g = Convert.ToDouble(textBox14.Text);
    t = Convert.ToDouble(textBox19.Text);

or may be it should be something like

    z = Convert.ToString(comboBox1.SelectedValue);
   d = Convert.ToDouble(checkBox1.Checked);

Comments

[Jason Kats]

The given input for all the textBoxes are numbers while the given input for the combobox is letters.

[Anurag_Soni]

you can find more detail about error in this link :stackoverflow.com/questions/12269254/…