6.9.6 Date Calculations

You can perform calculations with data types other than money or real. When you use date fields in a formula, you can compare two date fields with each other. Subtracting one date field from another results in the number of days between the two dates. Adding a number to a date field gives the date that many days past the date in the date field. Subtracting a number from a field of type date gives the date that many days before the date in the field. Figure 6 shows some calculated fields examples using dates.

Form Name ex6

Data File

Beginning form no Unique records no

Repeating form no Append form no

Freeze form no Additional form no

Required form no for one record

Next form name ex6

Field name date1 Field length 8

Entry Allowed yes Input required no

In Data File no Invisible no

Edit/Match test date1 < oldest "date too old"

Edit Data Type date

Field name diff Field length 7

Entry Allowed no Input Required no

In Data File no Invisible no

Calculation date1-today

Edit Data Type integer

Field name greater Field length 3

Entry Allowed no Input required no

In Data File no Invisible no

Calculation date1>today

Edit Data Type boolean

Field name date2 Field length 8

Entry Allowed no Input required no

In Data File no Invisible no

Calculation date1+5

Edit Data Type date

Field name today Field length 8

Entry Allowed no Input required no

In Data File no Invisible no

Initial value TODAY

Edit Data Type date

Field name oldest Field length 8

Entry Allowed no Input required no

In Data File no Invisible no

Initial value 1/1/1900

Edit Data Type date

Field name newest Field length 8

Entry Allowed no Input required no

In Data File no Invisible no

Initial value TODAY

Edit Data Type date

Figure 6

The today field has an initial value of TODAY, Which form replaces with the current date. This field is used for calculations with the entered date field, date1. Note again the use of the Edit Field Types field to declare the data type of each field.

The two fields oldest and newest contain initial values that represent the oldest and newest valid values for the date1 field. The date1 field is edited with the following formula

test date1 < oldest "date to old"

In a real application, you would make the today, oldest, and newest fields Invisible yes, so the operator would not see them.

The same kinds of calculations can be done with time fields. Two time fields may be compared with each other. Subtracting one time field from another results in the number of seconds between the two times. Adding a number to a time field gives the time that many seconds past the value in the time field. Subtracting a number from a time field gives the time that many seconds before the time in the field.