Automatically format payment amount entry in C#

Introduction

For end-users, it is much easier if they could enter the digits from a numeric keypad, and the currency format automatically applies, instead of entering a decimal point and numbers!

Background

In many PoS software applications (or similar environments), a payment screen requires a “payment amount entry.” Payment values (currency) almost always include a decimal point. So, if we don’t handle the decimal point and leave it to the user, it could (it will !) become a point of failure. When the user enters more than one decimal point or adds the decimal point where it changes the total amount (A $10.25 payments becomes $102.50) So, you either have to check the value or catch it at keypress level. A better method is to manage it at the entry point!

Using the code

On a Windows form, add buttons and build your “Price numeric keypad” . I have used a TableLayoutPanel of 4×4. Add a Textbox under the keypad grid, for the output.

I have introduced a public string, which decides what role our keypad will be playing:

public string numberRole = "MONEY" ;

“Money” role will set the stage for a payment value where a two digits decimal will be applied. For instance, if the amount is 10.25, we will have the followings:

step 1: 0.01

step 2: 0.10

step 3: 1.02

step 4: 10.25

“DIGITS” role will turn our keypad into a numeric, without the decimal point.

I also control the number of decimal points and also decimal digits(default is 2).

MakeAmount is the critical player in this code.

private void MakeAmount(string amountTxt)
    {
        decimal meanWhile;
        txtValue.Text = txtValue.Text + amountTxt;
        if (txtValue.Text.Length == 1)
        {
            txtValue.Text = "0.0" + txtValue.Text;
        }
        if (txtValue.Text.Length > 4)
        {
            meanWhile = Convert.ToDecimal(txtValue.Text) * 10;
            txtValue.Text = meanWhile.ToString("G29");
        }
    }

As you can see, it depends on what we have; the decimal points get moved.
For every digit, we have the same process, Except for zero, which we need to check a few things, all other Click events are similar:

private void num2_Click(object sender, EventArgs e) 
{ 
   if (numberRole == "DIGITS") 
     {
       txtValue.Text = txtValue.Text + "2" ; 
      } else MakeAmount(num2.Text);
 }

And for zero:

private void num0_Click(object sender, EventArgs e)
       {
           decimal meanWhile;
           if (numberRole == "DIGITS")
           {
               txtValue.Text = txtValue.Text + "0";
           }
           else
           {
               txtValue.Text = txtValue.Text + "0";
               if (txtValue.Text.Length == 1)
               {
                   txtValue.Text = "0.0" + txtValue.Text;
               }
               if (txtValue.Text.Length >= 4)
               {
                   meanWhile = Convert.ToDecimal(txtValue.Text) * 10;
                   txtValue.Text = meanWhile.ToString("G29");
               }
               if (Convert.ToDecimal(txtValue.Text) < 1)
               {
                   txtValue.Text = txtValue.Text + "0";
               }
               if (txtValue.Text.IndexOf(".") < 0)
               {
                   txtValue.Text = txtValue.Text + ".00";
               }
               if (Convert.ToDecimal(txtValue.Text) > 1 && (txtValue.Text.Length - txtValue.Text.IndexOf(".") - 1 == 1))
               {
                   txtValue.Text = txtValue.Text + "0";
               }
           }
       }

The following demonstrates how you call your price numeric keypad:

numberpad showNumber = new numberpad();
showNumber.numberRole = "MONEY";

As you can see, this calls for a “Money” format.
And if you need a numeric keypad, call your function with “DIGITS”:

numberpad showNumber = new numberpad();
showNumber.numberRole = "DIGITS";