C# How to Fix Error: 'Input string was not in a correct format.' in Textbox

Question

In the code below, I'm trying to validate the Textbox (txt_quantity and txt_discount)

But instead of getting this MessageBox.Show("Cannot be empty"); I'm getting the error of

('Input string was not in a correct format.')

Did i forgot something here?

txt_quantity(INTEGER)

txt_discount(DECIMAL)

decimal Discount, DiscountTotal, Discountgiven, Total;
int Cost, Quantity, ID;       
byte[] data;
public void Imagedisplay()
{
    using (var con = SQLConnection.GetConnection())
    {
        using (var selects = new SqlCommand("Select * from employee_product where Codeitem =@Codeitem ", con))
        {
            selects.Parameters.Add("@Codeitem", SqlDbType.VarChar).Value = _view.txt_code.Text;
            using (var reader = selects.ExecuteReader())
            {
                while (reader.Read())
                {
                    data = (byte[])reader["Image"];

                    Cost = Convert.ToInt32(reader["Unitcost"]);
                    Convert.ToInt32(DiscountTotal);
                //  This is where i'm getting the error at  
                    Quantity = Convert.ToInt32(txt_quantity.Text);
                    Discount = Convert.ToDecimal(txt_discount.Text); //
                    Discountgiven = Cost * (Discount / Convert.ToDecimal(100));
                    DiscountTotal = Cost - Discountgiven;
                    Total = DiscountTotal * Quantity;
                }

            }
        }
    }
}

private void btn_ok_Click(object sender, EventArgs e)
{
    Imagedisplay();
    using (var con = SQLConnection.GetConnection())
    {
        if (string.IsNullOrEmpty(txt_quantity.Text) || string.IsNullOrEmpty(txt_discount.Text))
        {
            MessageBox.Show("Cannot be empty");
        }
        else
        {                    
                using (var command = new SqlCommand("Insert into product_result (Date, Image, Code, Name, Price, Discount, Quantity, Total) Values (@Date, @Image, @Code, @Name, @Price, @Discount, @Quantity, @Total)", con))
                {                         
                    command.Parameters.Add("@Date", SqlDbType.VarChar).Value = date;
                    command.Parameters.Add("@Image", SqlDbType.VarBinary).Value = data;
                    command.Parameters.Add("@Code", SqlDbType.VarChar).Value = _view.txt_code.Text.Trim();
                    command.Parameters.Add("@Name", SqlDbType.VarChar).Value = _view.txt_name.Text.Trim();
                    command.Parameters.Add("@Price", SqlDbType.VarChar).Value = _view.txt_price.Text;
                    command.Parameters.Add("@Discount", SqlDbType.Decimal).Value = txt_discount.Text.Trim();
                    command.Parameters.Add("@Quantity", SqlDbType.Int).Value = txt_quantity.Text.Trim();
                    command.Parameters.Add("@Total", SqlDbType.Decimal).Value = Total;
                    command.ExecuteNonQuery();
                    Totals();                      
                }
                using (var selects = new SqlCommand("Update employee_product set quantity = quantity - @Quantity where Codeitem= @Codeitem", con))
                {
                    selects.Parameters.Add("@Codeitem", SqlDbType.VarChar).Value = _view.txt_code.Text;
                    selects.Parameters.Add("@Quantity", SqlDbType.Int).Value = txt_quantity.Text;
                    selects.ExecuteNonQuery();
                    this.Close();                          
                }                   
            _view.Display();
        }
    }          
}

What is the variable DiscountTotal and what is its value while debugging? — Aldert
– Aldert, Commented Sep 8, 2018 at 15:33
I'm passing the results of Cost * (Discount / Convert.ToDecimal(100)) to that variable DiscountTotal, the value of it is 0 while debugging — Anonymous
– Anonymous, Commented Sep 8, 2018 at 15:38

Handbag Crab · Accepted Answer · 2018-09-08 16:19:49Z

2

Use a NumericUpDown instead of a textbox to capture integer/decimal values. It handles all the validation for you stopping users from entering non-numeric values. You can set the maximum and minimum values you require and you don't have to worry about no values being entered as the NumericUpDown will always have a default value.

If you're using integers then you just need to cast to an int when you retrieve the value, otherwise it returns a decimal. So your code would be:

Quantity = Convert.ToInt32(numericupdown1.Value);
Discount = numericupdown2.Value;

If you're hellbent on using textboxes then you need to remove whitespace with .Trim()

Quantity = Convert.ToInt32(txt_quantity.Text.Trim());

And use int.TryParse instead;

int value = 0;
if (int.TryParse(txt_quantity.Text.Trim(), out value)
{
    // Successful conversion so value now contains your integer
}

You can do the same with decimals.

edited Sep 8, 2018 at 16:19

answered Sep 8, 2018 at 16:14

Handbag Crab

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1 Comment

Anonymous Over a year ago

Thank you so much. I really really appreciate it

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