输入的字符串格式不正确C＃

Question

I want to multiply the text value and combo box value and display it in a orderprice textbox the data types that I use in sql are 'float' for all of these

private void cb_oqty_SelectedIndexChanged(object sender, EventArgs e)
{
    int orderprice;
    int proprice=Convert.ToInt16(txt_oprice.Text);
    int quantity = Convert.ToInt16(cb_oqty.SelectedItem);

    orderprice = proprice * quantity;
    txt_orderprice.Text = Convert.ToString(orderprice);
    txt_orderprice.Update();                                
}

Answer 1

Use int.TryParse to see if the text can be converted first. That error seems to point to text not being able to be converted to int.

int orderprice = 0;
int proprice = 0;
int quantity = 0;

if (int.TryParse(txt_oprice.Text, out proprice) && int.TryParse(cb_oqty.SelectedValue.ToString(), out quantity))
{
    // It was assigned.
    orderprice = proprice * quantity;
}
else
{
    //Error
}

Also the cb_oqty.SelectedItem will not convert to an int as it is an Object. you need to use SelectedValue.

Answer 2

If your SQL datattype is float, your C# datatype should be float as well:

    private void cb_oqty_SelectedIndexChanged(object sender, EventArgs e)
    {
        var proprice = Convert.ToSingle(txt_oprice.Text);
        var quantity = Convert.ToSingle(cb_oqty.SelectedItem);

        var orderprice = proprice * quantity;
        txt_orderprice.Text = orderprice.ToString();

        // this does not do what you think it does. You can remove this line.
        txt_orderprice.Update();
    }

Better would be using the TryParse method.