One Form MVD app (Page 1 of 2)

Hello AD1408,

I worked a little on your project.

I am not an expert in this 'financial stuff' so I based my work on your calculated fields definitions in the database table.

The main structure of the program is there, but keep in mind that there is not data control in the script. For example, what should happen if one or more of the fields are left empty --> should the calculations be performed or should the user receive a warning ?

I commented the code so that you will find your way back through it, but it's quite simple.

1- Declare your variables with care (type)
2- Assign your variables to your edit fields
3- Code your calculations linked to the 'on click' event of the button (eventually adding controls with if /then)
4- Display the results in the correct edit fields

Have fun and do not hesitate if you have more questions

Cheers

Mathias

Hello AD1408,

Hooooooo, that's a tricky question !! I love that !

I adapted the code for the purpose you describe, but here is a little explanation :

What you want is make sure that the 4 edit fields ARE NOT empty.

To do that, YOU CAN NOT use a comparison with NULL or NIL or even with 0 :
- NIL means the variable if of type unknown, which is not true because you declared your variables as real
- NULL (IS NULL or = NULL) could be used, but not in your case because 0 value is acceptable
- For the same reason, you can not use 0 because in some case this value is acceptable.

The solution ?

You declared your variables as real, but they display in edit fields which contain text (even if you specified numbers only). So what we are going to test is that those edit fields are not empty. To do that, you can use :

Form1.Edit1.Text <> '';

This will make sure that the edit field is not empty, or

Length(Form1.Edit1.Text) <> 0;

which will test that the length of the content of the edit field is not 0

And if you want to be really thorough on your test (because some of your fields or not marked as Numbers Only), you could also make sure that white-spaces are taken into account, because they count as characters with the Trim command.
This command erases leading and trailing white-spaces.

Trim(Form1.Edit1.Text) <> '';

to make sure that the trimed content is not empty
or

Length(Trim(Form1.Edit1.Text)) <> 0;

to make sure that the Length of the Trimed content is not equal to 0 (trim before counting the length)

Now, unfortunatly, this is not enough in your case, because of the formula you use : there is a division in your second formula, and you can not divide by 0 (well, you can, but the NaN result does not interest you).

So there is a another serie a test to conduct before obtaining the result.

I added another variable in your code, that I called Divisor. Divisor is the result of

SLossPips * StdLotPipValue

If the result of this operation is 0, we know that the result of

(AccBalance * RiskPercent / 100) / Divisor;

will give you an error (the famous "invalid floating point operation you had previously).

The final code structure I opted for is like :

if any of the 4 edit fields is empty then
        begin
            Display a warning
        end
    else if none of the fields are empty then
        begin
            if Divisor = 0 then
                   begin
                         Display a Warning
                    end
                else if Divisor <> 0 then
                    begin
                         Perform the calculation and display the results
                    end;
        end;

Another possible approach would be to test that the two last edit fields are NOT EMPTY and NOT equal to 0, that(s up to you.

Hope this helped

Cheers

Mathias

Hello Adam, Hello Mathias,
I was just having a look at your project and there are a couple of points (and if you know this already, just ignore me - ha ha!).
You need to understand that calculated fields are not actual fields that are stored in tables - have a look at screenshot 1.jpg in the attachment .  Calculated fields are just empty containers that temporarily store the result of calculations based on actual fields in the table.  This is why, in your very first attempt, the calculation was not being done - you have no 'save' button so no actual fields are being written to the table and therefore, if you don't have any actual fields written to the table, there is no data to perform the calculation on.
If you understand this, you see that with Mathias' solution (which works perfectly) you don't need a table defined at all.  It uses the edit fields from Form1 to input values, then performs calculations solely within the script and then outputs the result back to Form1.
Maybe you'll find the attachment of interest - it takes another approach and actually saves your input fields to the table and, because it then has some actual data to use, can perform the formulae defined in your calculated fields and can then display the result back to you.
It doesn't matter which approach you use but maybe seeing the two helps you to better understand the advantages and disadvantages of calculated fields against doing calculations in a script.
Derek.

Hi Mathias
LOL! - yes, I noticed a spelling mistake so I delete and reposted!
Yes, for me 'minimalist' = EASY!! and less mistakes for me to make.
Derek.

Hello Adam,
If you have defined your fields as 'not null', then standard MVD will check that something has been entered into those fields - but 0 is allowed (and may well be valid).
However, what you could do in Form1 of your example, is to untick the 'currency' object property for your two currency fields (see attached screen shot) so that when you run the application, all 4 fields (2 currency, 1 real and 1 integer) display as blank;  at least then the User has to make the conscious decision to enter a value of 0 (rather than it defaulting  to 0 as it does when the 'currency' property is left ticked).  It is perhaps a bit less rigorous than the error checking that Mathias suggested to you but it can be done quickly and with no scripting.
To my knowledge, the message "This field is required......" that you get when a field has been left blank, is a standard message that cannot be amended.  It is 'switched on' when you configure the 'save' button on your forms.
Derek.

Hi Mathias,

I have tried to add other calculators with your code guidance but couldn't get it work. Please see, if you can get around to make them work. Btw, Your commenting on code is great. They help me a lot.

Hi Mathias,

Thank you so much for the info above. I love your instructions. You are a great teacher.

I got pivots calc compiled.

Working on CAGR calc... Once finished I'll upload it for your inspection - hopefully without bugs.

I think I got the Divisior bit working, not 100% sure tho.

However, on formula front no success. Math formula I'm trying implement is:

y = a(1 + r)^x

where:
y = future compounded value
a = initial value
r = growth rate
x = number of periods

I got the following object pascal implementation from another forum:

uses
  Math;
 
function CAGR(initial_value, grouth_rate, number_of_periods: double): double;
begin
  result := initial_value * Power(( 1 + grouth_rate), number_of_periods);
end;
 
begin
  writeln(CAGR(5.1, 10.4, 2.2):0:2);
  readln();
end.

Unfortunately, I couldn't implement it in MVD.

Thanks  for the info Lee.....

I'm not clear about variables and formula in your explanation. Actual formula needs to be used in this project code is:

OutputFutureValue := InitialValue * (1 + GrowthRate) ^ Periods; 

Problem is I couldn't work out power (^) part in script.

Could you not put in project code which starts at line 200 or into code below?

//CALCULATIONS
procedure Form1_Button3_OnClick (Sender: string; var Cancel: boolean);
var    //---> First declare your variables (pay attention to the type, integers take no decimals, real can have decimals and so on ...)

    //INPUT VARIABLES
    InitialValue : Currency;
    Periods, GrowthRate : Real;

    //OUTPUT VARIABLES
    OutputFutureValue : Currency;


begin
    //---> Second, assign the variables you have declared to your edit fields
    //Input Variables
    InitialValue := Form1.EdInitialValue.Value;
    Periods := Form1.EdPeriods.Value;
    GrowthRate := Form1.EdGrowthRate.Value;


    if (Trim(Form1.EdInitialValue.Text) = '') OR  (Trim(Form1.EdPeriods.Text) = '') OR  (Trim(Form1.EdGrowthRate.Text) = '') then //if any of the field is empty
        begin
            Cancel := True; //Stop the operation
            ShowMessage('All fields marked with an asterisk (*) are required. Calculation can only be performed when all required fields are filled.'); //display the warning
        end

    else //None of the fields are empty, let's continue
        begin

            //---> Third, perform your calculations

                        OutputFutureValue := InitialValue * (1 + GrowthRate) ^ Periods;
                        Form1.EdOutputFutureValue.Value := OutputFutureValue;

Hi Lee,

I couldn't get your formula to compile. However, thank you very much for the effort.

Perhaps somebody here can offer the solution....................................

that will do it a whole lot easier. i was doing it with a for/next loop which apparently neither one of us knows how to code in MVD

thanks
lee

Hi.
i think it should be OutputFuturevalue := InitalValue * Power((1 + GrowthRate), Periods);

the other way included initalvalue in the power and i dont think that is what he wanted.

lee