A computed field or cell displays the result of an arithmetic formula that may include operators, variables and constants. By default, the ComputedField property is empty. If the the ComputedField property is empty, the property have no effect. If the ComputedField property is not empty, all cells in the column, that have the CellCaptionFormat property on exText, uses the same formula to display their content. For instance, you can use the CellCaptionFormat property on exHTML, for cells in the column, that need to display other things than column's formula, or you can use the CellCaptionFormat property on exComputedField, to change the formula for a particular cell.

Use the CellCaptionFormat property to change the type for a particular cell. Use the CellCaption property to specify the cell's content. For instance, if the CellCaptionFormat property is exComputedField, the Caption property indicates the formula to compute the cell's content. 

The Def(exCellCaptionFormat) property is changed to exComputedField, each time the ComputeField property is changed to a not empty value. If the ComputedField property is set to an empty string, the Def(exCellCaptionFormat) property is set to exText. Call the Refresh method to force refreshing the control.

The expression may be a combination of variables, constants, strings, dates and operators.  A string is delimited by ", ` or ' characters, and inside they can have the starting character preceded by \ character, ie "\"This is a quote\"". A date is delimited by # character, ie #1/31/2001 10:00# means the January 31th, 2001, 10:00 AM. The expression supports also immediate if ( similar with iif in visual basic, or ? : in C++ ) ie cond ? value_true : value_false, which means that once that cond is true the value_true is used, else the value_false is used. Also, it supports variables, up to 10 from 0 to 9. For instance, 0:="Abc" means that in the variable 0 is "Abc", and =:0 means retrieves the value of the variable 0. For instance, the "len(%0) ? ( 0:=(%1+%2) ? currency(=:0) else `` ) : ``" displays the sum between second and third column in currency format if it is not zero, and only if the first column is not empty. As you can see you can use the variables to avoid computing several times the same thing ( in this case the sum %1 and %2 .

The supported binary arithmetic operators are:

• * ( multiplicity operator ), priority 5
• / ( divide operator ), priority 5
• + ( addition operator ), priority 4 ( concatenates two strings, if one of the operands is of string type )
• - ( subtraction operator ), priority 4

The supported unary boolean operators are:

• not ( not operator ), priority 3 ( high priority )

The supported binary boolean operators are:

• or ( or operator ), priority 2
• and ( or operator ), priority 1

The supported binary boolean operators, all these with the same priority 0, are :

• < ( less operator )
• <= ( less or equal operator )
• = ( equal operator )
• != ( not equal operator )
• >= ( greater or equal operator )
• > ( greater operator )

Obviously, the priority of the operations inside the expression is determined by ( ) parenthesis and the priority for each operator. 

The supported conversion unary operators are:

• type (unary operator) retrieves the type of the object. For instance type(%0) = 8 specifies the cells that contains string values. 

  Here's few predefined types:

   

  • 0 - empty ( not initialized )
  • 1 - null
  • 2 - short
  • 3 - long
  • 4 - float
  • 5 - double
  • 6 - currency
  • 7 - date
  • 8 - string
  • 9 - object
  • 10 - error
  • 11 - boolean
  • 12 - variant
  • 13 - any
  • 14 - decimal
  • 16 - char
  • 17 - byte
  • 18 - unsigned short 
  • 19 - unsigned long
  • 20 - long on 64 bits 
  • 21 - unsigned long on 64 bites

   

• str (unary operator) converts the expression to a string
• dbl (unary operator) converts the expression to a number
• date (unary operator) converts the expression to a date

Other known operators for numbers are:

• int (unary operator) retrieves the integer part of the number
• round (unary operator) rounds the number ie 1.2 gets 1, since 1.8 gets 2
• floor (unary operator) returns the largest number with no fraction part that is not greater than the value of its argument
• abs (unary operator) retrieves the absolute part of the number ie -1 gets 1, 2 gets 2

Other known operators for strings are:

• len (unary operator) retrieves the number of characters in the string
• lower (unary operator) returns a string expression in lowercase letters
• upper (unary operator) returns a string expression in uppercase letters
• proper (unary operator) returns from a character expression a string capitalized as appropriate for proper names
• startwith (binary operator) specifies whether a string starts with specified string
• endwith (binary operator) specifies whether a string ends with specified string
• contains (binary operator) specifies whether a string contains another specified string

Other known operators for dates are:

• time (unary operator) retrieves the time of the date
• shortdate (unary operator) formats a date as a date string using the short date format
• longdate (unary operator) formats a date as a date string using the long date format
• year (unary operator) retrieves the year of the date
• month (unary operator) retrieves the month of the date ( 1, 2,...,12 )
• day (unary operator) retrieves the day of the date ( 1, 2,...,31 )
• yearday (unary operator) retrieves the number of the day in the year, or the days since January 1st ( 0, 1,...,365 )
• weekday (unary operator) retrieves the number of days since Sunday ( 0 - Sunday, 1 - Monday,..., 6 - Saturday )
• hour (unary operator) retrieves the hour of the date ( 0, 1, ..., 23 )
• min (unary operator) retrieves the minute of the date ( 0, 1, ..., 59 )
• sec (unary operator) retrieves the second of the date ( 0, 1, ..., 59 )

Samples:

1. "1", the cell displays 1
2. "%0 + %1", the cell displays the sum between cells in the first and second columns.
3. "%0 + %1 - %2", the cell displays the sum between cells in the first and second columns minus the third column.
4. "(%0 + %1)*0.19", the cell displays the sum between cells in the first and second columns multiplied with 0.19.
5. "(%0 + %1 + %2)/3", the cell displays the arithmetic average for the first three columns.
6. "%0 + %1 < %2 + %3", displays 1 if the sum between cells in the first  two columns is less than the sum of third and forth columns.
7. "proper(%0)'" formats the cells by capitalizing first letter in each word
8. "currency(%1)'" displays the second column as currency using the format in the control panel for money
9. "int(date(%1)-date(%2)) + " D " + round(24*(date(%1)-date(%2) - floor(date(%1)-date(%2)))) + "H"'" displays interval between two dates in days and hours

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