How to declare a variable in an HTML page?

How to declare a variable in an HTML page?

I seem to have forgotten (or never knew) how to declare a variable as float or decimal. If I use the following statement:

invoice_total = 0;

and then go on to use this local variable as follows:

invoice_total = invoice_total + (sales_invoice_item_record.Unit_Price * sales_invoice_item_record.Quantity);

the app builder tells me the variable, 'invoice_total' is defined as BIGINT and incompatible with the other fields in the statement which are both defined as decimal in the form.

I have looked for this in the Deluge Reference Guide but can't find the answer.

Can anyone help me with this simple question?