Category: Program Features

A logic expression is an expression that, when evaluated, yields either a $True or a $False result.

Logic expressions are subdivided into conditional expressions and Boolean expressions.

How To Construct Conditional Expressions

A conditional expression is a complex logic expression that consists of two value expressions and an associated conditional operator. The conditional operator performs a designated comparison of the value expressions and returns the result $True or $False. Conditional expressions can be combined into Boolean expressions.

The conditional operators are

= (equals)

<> (not equals)

< (less than)

> (greater than)

<= (less than or equals)

>= (greater than or equals)

[NOT] BETWEEN

[NOT] IN

[NOT] LIKE

Examples of Conditional Expressions

EmpNum < 1254

DeptNum >= EmpNum

First Name = “Smith”

DeptDesc <> “Sports”

EmpNum between 1000 and 2000

LastName like “%ith%”

Event.EventName in (“F1”, “F2”, “Escape”)

ProdCode not between 542 and 863

LastName not in (“Smith”, “Jones”)

FirstName not like “Sm%”

How To Use Boolean Expressions

A Boolean expression is a complex logic expression that consists of one or more conditional expressions and an associated Boolean operator. The Boolean operator performs a Boolean operation on the $True or $False values returned by the conditional expression(s) and returns the result $True or $False.

The Boolean operators are

AND

OR

XOR

NOT

Examples of Boolean Expressions

LastName = “Allan” or FirstName = “Allan”

DeptNum = “Sports” and Salary > 45000 and LastName = “Smith”

not Salary > 45000

See Also

$and

$not

$or

Truth Tables

The syntax of a call to a procedure is

procname («expression»)

Parameters

Comments

The list of expressions must be enclosed in parentheses; even when no expressions are required, the parentheses must still appear.

At the prompt level, you can issue a call to the main procedure of any procedure program.

Within a procedure program, you can issue a call to

• any local procedure in the current program

• the main procedure in the current program

• the main procedure in any other procedure program

Any procedure in a procedure program can issue a call to itself.

In a call to a procedure, you must supply one expression for each parameter specified in the PROCEDURE or LOCALPROCEDURE command that describes the called procedure. The number and type of expressions listed in the call to a particular procedure must match the number and type of parameters in the PROCEDURE command in order for the procedure to execute. The value of expression can be assigned to the corresponding parameter (IN parameters), or expression can take on the value of the corresponding parameter when the procedure ends (OUT parameters), or both (INOUT parameters).

When you specify more than one expression, each must be separated from the next by a comma.

See Also

Conventions

LOCALPROCEDURE

PROCEDURE

TRANSFORM

The available pattern symbols for constructing numeric validation rules are

• digits used to form specific numbers. Numbers indicate value(s) to which the input data must conform.

• +, – used to specify the sign of a number.

• period used as a decimal point.

The available syntax characters for constructing numeric validation rules are

Examples of Numeric Validation Rules

The following table contains examples of numeric validation rules, and the values that can be legal or illegal under those rules:

Names for objects defined in the Object Dictionary must conform to the following conventions:

• The name can be from 1 to 18 characters in length.

• The name can contain only letters (a-z, A-Z), digits (0-9), dollar signs ($), and underscores (_).

• The name must begin with a letter or a dollar sign.

• Most names must be unique among objects of the same type in the same application directory. (Note that the software is case-insensitive: ABC and abc are the same name.) For more information, see the documentation for your operating system.

• The name does not duplicate words reserved to the software’s use, such as a command or function keyword (CREATE, $isalphabetic).

Examples of Object Names

Examples of valid names are

• myfile98

• x99

• a

• ProjectControl56

• x_7b

• date

• $i

Compare these to the following invalid names:

• 98myfile

• 99

• a+

• x%@

• ProjectControl 56/8

• $Date

When certain atomic expressions (variable name, field name, form field name, or formal parameter name) are used before being assigned values, or if the values are unknown, those expressions are considered to be $Null.

$Null is a property indicating a state of valuelessness; $Null is not itself a value. The null string is a value and is therefore not the same as the $Null property.

An arithmetic or functional expression that includes a $Null argument or operand always evaluates to $Null.

A logic expression that includes a $Null operand always evaluates to $False.

Because $Null is not a value, you cannot use the conditional operators = (Equals) and <> (Not Equals) to determine if an expression is $Null. Instead, the operator IS [NOT] [$]NULL is used as shown in the following example:

Salary is $null

Salary is not $null

Note: $Null can be written without the dollar sign.

The available pattern symbols for constructing date validation rules are

• digits used to form numbers that constitute valid dates. The input data must conform to the specified date(s).

The available syntax characters for constructing date validation rules are

Examples of Date Validation Rules

Date values are stored in the format YYYYMMDD. Use DataMask to control how the date is to be input or displayed in the field. So the rule can be expressed as follows:

19990101-19991231

Input values that are accepted as legal include any date during 1999.

The results of value expressions are rounded automatically, but only after the entire expression has been evaluated. (During evaluation, full decimal values are used.)

The final result takes on the number of decimal places found in the operand with the most decimal places.

The rounded result is further rounded if it is being assigned to a named constant, a variable, a field, or a form field defined to contain fewer decimal places.

To force rounding in particular circumstances, use the $round function.

Examples of Rounding

5/2

Result is 3.

5/2.0

Result is 2.5.

1+1.01

Result is 2.01.

1.01+(5/2)

Result is 3.51.

Integer=1.01+(5/2)

Result is 4 if Integer is defined to contain no decimal places.

Within a quoted character string, a backslash immediately followed by two characters that are either digits from 0 to 9 or letters from A(a) to F(f) are treated as a hex code. The text string containing the hex code must be enclosed in quotation marks.

Example of Using Hex Codes

set output printer
output “F”;    % selects a condensed font
…report commands…
output “12”;    % restores regular font
set output terminal

The Alt+F6 keystroke combination cycles the user through all available windows if the current window is not modal. Its effect is similar to clicking the mouse to make a non-current window current.

The Ctrl+F6 keystroke combination cycles through all available sibling windows of a child window.

A named constant is a programming object defined in the Object Dictionary for the application. The constant’s value is part of its definition.

By using named constants in place of literal constants in application programs, you ensure that a constant’s value can be quickly, easily, and universally changed, if necessary.