Instant calculation

Hi ehwagner,

Excellent. Thanks a lot.............

I liked the way you did; without changing field type to calculated on dbTable.

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Edit:

I checked it bit more and noticed following issues:
1. When numbers typed in edit1, it shows on edit3 as a minus numbers. Since calc needs two numbers, perhaps we don't print in edit3 before entering numbers in edit2

2. When typed a minus numbers, calculations are not performed correctly. For example:
Edit1 50.00, Edit2 -100.00 produces -150.00 instead of -50.00

3. I think we need cancel := when user types minus numbers  in Edit and message box saying 'Starting balance must be bigger than zero'

Shortcomings are on my side. I should have specified all these in the first post. My apologies...

Hi Dmitry,

Thanks a lot.....

Example is fine for multiplications but on adding and subbing I encounter issues. Perhaps my logic is rotten.
The following code works OK:

//edit1 is starting_balance
//edit2 is ending_balance
//edit3 is profit_loss (calculated field)

procedure CalculateTotal;
begin
    Form1.Edit3.Value := Form1.Edit1.value * Form1.Edit2.Value;
    If Form1.Edit3.Value <0 then Form1.Edit3.Font.Color := clRed else Form1.Edit3.Font.Color := clWindowText;
end;


procedure Form1_Edit1_OnChange (Sender: string);
begin
    CalculateTotal;
end;

procedure Form1_Edit2_OnChange (Sender: string);
begin
    CalculateTotal;
end;

However, when ending balance is minus figure then calculation is incorrect. One can start with $100.00 and ends up with -$50.00. In this situation shouldn't result show -$150.00?

Also wanted to prevent user entering a minus figure in Edit1 with following code but didn't work:

begin
    If Form1.Edit1.Value <0 then
    begin
    Cancel := True;
    ShowMessage('Starting balance value must be bigger than zero');
    end;
end;

Evening Adam,

Getting the calculation to fire off correctly is trickier than you first think - what sequence is the user entering the figures in, do they 'tab' or 'backtab', do they backspace out a field (leaving it empty / not null / zero).
Anyways, this is the way I think I'd do it.  Probably other ways as well.
Derek.

Hi ehwagner,
Hi Derek,

Thanks for the latest updates.....

Lets consider real life situation.  For instance, I can start a business with borrowed money (minus starting balance) or my own money (plus starting balance) but I cannot start with zero (this is where pop-up message should be applicable as 'Starting balance cannot be zero' in proper way of doing it. No message needed for ending balance as I can end with plus, minus or zero.

examples:
1. Starting balance 100, ending balance -50 calc profit / loss should show: -150
2. Starting balance 100, ending balance 0 calc profit / loss should show: -100
3. Starting balance -100, ending balance 25 calc profit / loss should show: -75
4. Starting balance -200, ending balance -100 calc profit / loss should show: -300
5. Starting balance 150, ending balance  175 calc profit / loss should show: 25
6. Starting balance 150, ending balance  125 calc profit / loss should show: -25

Form1.Edit3.Value := Form1.Edit2.value - Form1.Edit1.Value;

Since edit1 holds the base value shouldn't the above be like this:

Form1.Edit3.Value := Form1.Edit1.value - Form1.Edit2.Value;

On latest update, unfortunately instant display is gone. I assume it's due to waiting for user to enter ending balance value before calc takes place.

Hi Derek,

No doubt my logic on this math stuff not conventional and in standard math most likely wrong. What you did is correct according my previous posts, which I appreciate the sample you did. It'll definitely be useful for me. Thanks again.... I hope you and ehwagner can forgive my inconsistency in this matter.

With the latest post of mine, I tried to illustrate practical aspect of it, if it's doable.