Boolean Expressions
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A Boolean expression is an expression that evaluates to a Boolean value. Boolean expressions can take several forms. The simplest is the direct comparison of the value of a Boolean variable to a Boolean literal, as shown in this example:
If x = *True // Compares x to *True
// Insert code to execute if x= *True
Else // Insert code to execute if x= *False
EndIf
Note that the assignment statement x = True looks the same as the expression in the example, but it performs a different function and is used differently. In the above example, the expression x = True represents a value, and thus the = sign is interpreted as a comparison operator. In a stand-alone statement, it would be interpreted as an assignment operator and assign the value on the right to the variable on the left. The following example illustrates this:
If x = *True // Compare the value of x to *True
y = *False // Assign *False to variable y
EndIf
Comparison operators, such as =, < , > , <> , <= , and >=, produce Boolean expressions by comparing the expression on the left side of the operator to the expression on the right side of the operator and evaluating the result as true or false. For instance:
39 < 81 // Evaluates to *True
Comparison expressions can be combined using logical operators to produce more complex Boolean expressions. The following example demonstrates the use of comparison operators in conjunction with a logical operator:
x > y And x < 5000
In the example, the value of the overall expression depends on the values of the expressions on each side of the *And operator. If both expressions are true, then the overall expression evaluates as *True. If either expression is false, then the entire expression evaluates to *False.
Parenthetical Expressions
You can use parentheses to control the evaluation of Boolean expressions. Expressions enclosed by parentheses evaluate first. For multiple levels of nesting, precedence is granted to the most deeply-nested expressions. Within parentheses, evaluation proceeds according to the rules of operator precedence. For more information, see Operator Precedence in Encore RPG.