Input string was not in in correct format

Yes Thomas that's true, thank you so much and I really appreciate your help 

Thank you Prasad, it is the clear function that is causing the problem 

It's possible that the Clear() or fm.LoadCategory() methods might be causing issues, especially if they are clearing or reloading values in a way that interferes with subsequent event handlers. To investigate, let's look at what these methods do and make sure they don't inadvertently clear necessary data or trigger events that cause parsing to fail.

Please set breakpoints in these two methods and then click the Save button. Debug these methods to identify the cause of the error message.

Please share the code for Clear() as well here.

Hello Prasad Raveendran

The response that is coming from the combobox after trying your new code is saying that salesPrice and tax must be numeric value but I enter numeric value and it did save in the database as numeric value so how come this after save error response is coming

Hello Emmanuel,

My apologies. My first question should have been which C# version you are using. The syntax I provided was introduced in C# 7.0.

Here is the modified code. Please try and let me know

private void btn_Save_Click(object sender, EventArgs e)
{
    if (string.IsNullOrWhiteSpace(txt_Productname.Text) || 
        string.IsNullOrWhiteSpace(txt_CostPrice.Text) || 
        string.IsNullOrWhiteSpace(txt_SalesPrice.Text))
    {
        MessageBox.Show("Missing Information !!!");
        return;
    }

    decimal costPrice;
    decimal salesPrice;

    if (!decimal.TryParse(txt_CostPrice.Text, out costPrice) || 
        !decimal.TryParse(txt_SalesPrice.Text, out salesPrice))
    {
        MessageBox.Show("Cost Price and Sales Price must be numeric values.");
        return;
    }

    decimal profit = salesPrice - costPrice;

    try
    {
        if (MessageBox.Show("Please confirm if you want to save this product?", 
            "Confirm", MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes)
        {
            cn.Open();
            cm = new SqlCommand("INSERT INTO tblProduct(PCode,ProductDate,ProductName, Category, CostPrice,Profit,SalesPrice,Tax,TotalPrice,Barcode) " +
                "VALUES(@pCode,@productDate,@productName, @category, @costPrice,@profit,@salesPrice,@tax,@totalPrice,@barcode)", cn);
            cm.Parameters.AddWithValue("@pCode", txt_ProductCode.Text);
            cm.Parameters.AddWithValue("@productDate", dtProductDate.Value);
            cm.Parameters.AddWithValue("@productName", txt_Productname.Text);
            cm.Parameters.AddWithValue("@category", cbo_Category.Text);
            cm.Parameters.AddWithValue("@costPrice", costPrice);
            cm.Parameters.AddWithValue("@profit", profit);
            cm.Parameters.AddWithValue("@salesPrice", salesPrice);

            decimal tax;
            if (!decimal.TryParse(cbo_Tax.Text, out tax))
            {
                MessageBox.Show("Tax must be a numeric value.");
                cn.Close();
                return;
            }

            cm.Parameters.AddWithValue("@tax", tax);

            decimal totalPrice;
            if (!decimal.TryParse(txt_TotalPrice.Text, out totalPrice))
            {
                MessageBox.Show("Total Price must be a numeric value.");
                cn.Close();
                return;
            }

            cm.Parameters.AddWithValue("@totalPrice", totalPrice);
            cm.Parameters.AddWithValue("@barcode", txt_Barcode.Text);
            cm.ExecuteNonQuery();
            cn.Close();

            MessageBox.Show("Product has been successfully saved!", "POS", MessageBoxButtons.OK, MessageBoxIcon.Information);
            Clear();
            fm.LoadCategory();
        }
    }
    catch (Exception ex)
    {
        cn.Close();
        MessageBox.Show(ex.Message);
    }
}

private void cbo_Tax_SelectedIndexChanged(object sender, EventArgs e)
{
    try
    {
        decimal salesPrice;
        decimal tax;

        if (decimal.TryParse(txt_SalesPrice.Text, out salesPrice) && 
            decimal.TryParse(cbo_Tax.Text, out tax))
        {
            decimal total = (salesPrice * tax / 100) + salesPrice;
            txt_TotalPrice.Text = total.ToString("#,##0.00");
        }
        else
        {
            MessageBox.Show("Sales Price and Tax must be numeric values.");
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
}

Hello Thomas.

Please your format isn't working form me

Hello Prasad 

This is the error that is poping up

The combobox

C

The save button

The save buttons

I tried this way and it works for me: - 

CREATE TABLE Products (
    ProductID INT PRIMARY KEY,
    ProductName VARCHAR(100),
    Price DECIMAL(18, 2)
);

using System;
using System.Data.SqlClient;
using System.Windows.Forms;

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void buttonInsert_Click(object sender, EventArgs e)
    {
        try
        {
            decimal price = Convert.ToDecimal(textBoxPrice.Text);
            InsertData(price);
        }
        catch (FormatException)
        {
            MessageBox.Show("Please enter a valid decimal number for the price.");
        }
    }

    private void InsertData(decimal price)
    {
        string connectionString = "YourConnectionStringHere";
        string query = "INSERT INTO Products (ProductName, Price) VALUES (@ProductName, @Price)";

        using (SqlConnection connection = new SqlConnection(connectionString))
        {
            SqlCommand command = new SqlCommand(query, connection);
            command.Parameters.AddWithValue("@ProductName", "Sample Product");
            command.Parameters.AddWithValue("@Price", price);

            try
            {
                connection.Open();
                int result = command.ExecuteNonQuery();
                if (result < 0)
                    MessageBox.Show("Error inserting data into Database!");
                else
                    MessageBox.Show("Data inserted successfully!");
            }
            catch (Exception ex)
            {
                MessageBox.Show("Error: " + ex.Message);
            }
        }
    }
}

Mr. Emmaanuel

The problem as you are not converting the text value into decimal. try this -

Convert.ToDecimal(textBoxPrice.Text); 

This will solve the issue.

Could you please try this way.

Save Button Click Event

private void btn_Save_Click(object sender, EventArgs e)
{
    if (string.IsNullOrWhiteSpace(txt_Productname.Text) || 
        string.IsNullOrWhiteSpace(txt_CostPrice.Text) || 
        string.IsNullOrWhiteSpace(txt_SalesPrice.Text))
    {
        MessageBox.Show("Missing Information !!!");
        return;
    }

    if (!decimal.TryParse(txt_CostPrice.Text, out decimal costPrice) || 
        !decimal.TryParse(txt_SalesPrice.Text, out decimal salesPrice))
    {
        MessageBox.Show("Cost Price and Sales Price must be numeric values.");
        return;
    }

    decimal profit = salesPrice - costPrice;

    try
    {
        if (MessageBox.Show("Please confirm if you want to save this product?", 
            "Confirm", MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes)
        {
            cn.Open();
            cm = new SqlCommand("INSERT INTO tblProduct(PCode,ProductDate,ProductName, Category, CostPrice,Profit,SalesPrice,Tax,TotalPrice,Barcode) " +
                "VALUES(@pCode,@productDate,@productName, @category, @costPrice,@profit,@salesPrice,@tax,@totalPrice,@barcode)", cn);
            cm.Parameters.AddWithValue("@pCode", txt_ProductCode.Text);
            cm.Parameters.AddWithValue("@productDate", dtProductDate.Value);
            cm.Parameters.AddWithValue("@productName", txt_Productname.Text);
            cm.Parameters.AddWithValue("@category", cbo_Category.Text);
            cm.Parameters.AddWithValue("@costPrice", costPrice);
            cm.Parameters.AddWithValue("@profit", profit);
            cm.Parameters.AddWithValue("@salesPrice", salesPrice);

            if (!decimal.TryParse(cbo_Tax.Text, out decimal tax))
            {
                MessageBox.Show("Tax must be a numeric value.");
                cn.Close();
                return;
            }

            cm.Parameters.AddWithValue("@tax", tax);

            if (!decimal.TryParse(txt_TotalPrice.Text, out decimal totalPrice))
            {
                MessageBox.Show("Total Price must be a numeric value.");
                cn.Close();
                return;
            }

            cm.Parameters.AddWithValue("@totalPrice", totalPrice);
            cm.Parameters.AddWithValue("@barcode", txt_Barcode.Text);
            cm.ExecuteNonQuery();
            cn.Close();

            MessageBox.Show("Product has been successfully saved!", "POS", MessageBoxButtons.OK, MessageBoxIcon.Information);
            Clear();
            fm.LoadCategory();
        }
    }
    catch (Exception ex)
    {
        cn.Close();
        MessageBox.Show(ex.Message);
    }
}

Tax ComboBox SelectedIndexChanged Event

private void cbo_Tax_SelectedIndexChanged(object sender, EventArgs e)
{
    try
    {
        if (decimal.TryParse(txt_SalesPrice.Text, out decimal salesPrice) && 
            decimal.TryParse(cbo_Tax.Text, out decimal tax))
        {
            decimal total = (salesPrice * tax / 100) + salesPrice;
            txt_TotalPrice.Text = total.ToString("#,##0.00");
        }
        else
        {
            MessageBox.Show("Sales Price and Tax must be numeric values.");
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
}

LoadCategory method looks fine, but ensure that the category names in your tblCategory table are all valid strings and there's no unexpected data.

Final Notes

Parameter Types in SQL: Use the correct data types when adding parameters to your SQL command, especially for dates and decimals.

User Input Validation: Always validate user input before processing it, ensuring that non-numeric values don't cause exceptions when converting to numeric types.

Error Handling: Handle parsing errors gracefully to provide clear feedback to the user instead of allowing exceptions to occur.

Hello Mr. Thomas,

Please as I change the way you said it, this is the error that popup

Hello Thomas.

Error Message is this and the table struction

Mr. Emmmanuel FIADUFE

Can u show me a screenshot of the error. also check the stucture of the database table.

Regards, 

Hello Thomas,

I tried that format before but the error still came

Hello Kumar

  public void LoadCategory()
        {
            cbo_Category.Items.Clear();
            try
            {
                int i = 0;
                // dataGridView1.Rows.Clear();
                cn.Open();
                cm = new SqlCommand("select * from tblCategory", cn);
                dr = cm.ExecuteReader();
                while (dr.Read())
                {
                    i++;

                    cbo_Category.Items.Add(dr["CategoryName"].ToString());
                }
                dr.Close();
                cn.Close();
            }
            catch (Exception ex)
            {
                cn.Close();
                MessageBox.Show(ex.Message);
            }
        }

Dear Emmmanuel FIADUFE,

i strongly guess the below line of code is creating the problem.

 cm.Parameters.AddWithValue("@productDate", DbType.Date).Value = dtProductDate.Value;

please change the same as follows: -

cm.Parameters.AddWithValue("@productDate", dtProductDate.Value.ToString("yyyy-MM-dd"));

Hi,

Then you need to check in this method fm.LoadCategory();

Could you please share the code for this method ?