In VFP9 you would use CAST function. In prior VFP version for numeric fields there is

00000000.00 a way to create a field with precision.

.f. for logical
{} for dates
{:} for times.

If you need an Integer field or a memo field the only way is to create a cursor with one empty record and join with this cursor

select * from myTable, myCursor

>I build a cursor. Within that cursor I want to add a field. The thing is that I will use that field to do computations.
>
>For example:
>
>select Amount1, amount2, ResultComputation
>
>Amount1 and Amount2 are fields in a table. I want to create ResultComputation
>
>How do I create a field without knowing the value it will hold?
>
>For example what if I want that field to hold N(8,2)?
>
>As long as we're at it how would I create other kinds of fields
>
>For example :
>
>I know that for a logical I can do this : Select .t. as LogicalField
>I know that for strings I can do this : select space( 20) as StringField