C＃将输入的文本框值减去标签值

Question

I'm building these POS Desktop application in Windows form and it's almost done but i'm having problem in processing the customer bills.

To be specific:
SIMSProduct Usercontrol

• cart.lbl_price.Text = lbl_totalprice.Text;
  First the total of the customer bought is in lbl_totalprice.Text
  Next that total is used to ProcessCart Form which is the cart.lbl_price.Text
• lbl_price.Text is now successfully getting the value of lbl_totalprice.Text

ProcessCart Form

• txt_amount(Textbox) is where user input the pay value of customer that should be subracted to the lbl_price.Text which is fail.
• lbl_totalprice.Text corresponds to the output of subracted lbl_price and txt_amount which is fail too

Note: lbl corresponds to Windows form Label

The problem is when i tried to input to my txt_amount, let's say i input 5000 and that 5000 is not subracting the value of lbl_price, also the lbl_totalprice is equal to what i type to txt_amount. Below these code, What I've done wrong here ?, something that i should not made? or i forgot something ?. I hope someone would be able to help in these matter. Thank you

    public partial class SIMSProduct : UserControl
{
    ITEMCount item;
    ProcessCart cart;
    public SIMSProduct()
    {
        InitializeComponent();         
    }

 private void btn_process_Click(object sender, EventArgs e)
    {
        cart = new ProcessCart();
        cart.Show();
        cart.lbl_price.Text = lbl_totalprice.Text; 
    }
}

public partial class ProcessCart : Form
{     
    public ProcessCart()
    {
        InitializeComponent();
    }
 private void txt_amount_TextChanged(object sender, EventArgs e)
    {
        int value1;
        int value2;
        decimal value3;
        if (int.TryParse(lbl_price.Text.Trim(), out value1))
        {
            Total = Convert.ToInt32(lbl_price.Text);            
        }
        if (int.TryParse(txt_amount.Text.Trim(), out value2))
        {

            Paid = Convert.ToInt32(txt_amount.Text);          
        }
        lbl_totalprice.Text = (Paid - Total).ToString();
}

Answer 1

I think your issue is a casting issue. Looks like you're attempting to cast a decimal to an integer value. Try replacing with this code.

    public partial class SIMSProduct : UserControl
{
    ITEMCount item;
    ProcessCart cart;
    public SIMSProduct()
    {
        InitializeComponent();         
    }

 private void btn_process_Click(object sender, EventArgs e)
    {
        cart = new ProcessCart();
        cart.Show();
        cart.lbl_price.Text = lbl_totalprice.Text; 
    }
}

public partial class ProcessCart : Form
{     
    public ProcessCart()
    {
        InitializeComponent();
    }
 private void txt_amount_TextChanged(object sender, EventArgs e)
    {
        decimal value1;
        decimal value2;
        decimal value3;
        if (decimal.TryParse(lbl_price.Text.Trim(), out value1))
        {
            Total = Convert.ToDecimal(lbl_price.Text);            
        }
        if (decimal.TryParse(txt_amount.Text.Trim(), out value2))
        {

            Paid = Convert.ToDecimal(txt_amount.Text);          
        }
        if (decimal.TryParse(lbl_totalprice.Text.Trim(), out value3))
        {
            Change = Convert.ToDecimal(lbl_totalprice.Text);
        }
        Change = Paid - Total;
    }
}