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Chapter Four — Flow Control (continued)

4.8 ‘if’, ‘elseif’ and ‘else’ Statements

4.8.1 The If Condition

The if statement processes a single expression and then acts depending the on boolean result of that process. The expression can be simple or extremely complex, but in the end, must resolve to logical FALSE or TRUE. For example:

if (a == b) {

...

}

if (response != "YES") {

...

}

if ((a == b) && (b == c)) {

...

}

 

If the result is nonzero (TRUE), the statement or block of statements following the if statement will be executed. If the result is zero (FALSE), the statement or block of statements is skipped. In addition, an else conditional can be added to execute a statement or block of statements if the boolean expression results in a FALSE condition.

The elseif statement allows a series of conditions to be in the form of a cascade:

if (response == "YES") {

...

}

elseif (response == "NO") {

...

}

elseif (response == "CANCEL") {

...

}

else {

...

}

Unlike the first example, this comprises an interconnected set of conditions. If the response is false, the next elseif condition is tested and so on. An optional end else can be added for the end catch all.

4.8.2 Syntax and Structure

The if, elseif and else statements use the following formal syntax:

if (expression) {

statement(s)

}

[elseif (expression) {]

[statement(s)]

}

[else]

[statement(s)]

}

 

Zero or more elseif statements can be added, but the elseif must be associated with a preceding if block. The else statement is optional and when omitted, program execution will continue after the block if the expression is not true. The elseif and else statements must immediate precede the related conditional block.

4.9.3 The ‘else if’ Combination‡

[The else if combination of keywords can be used to test multiple conditions. This allows the programmer to create multiple different flow paths via a multiway branch, where different blocks of statements can be executed depending on the logical results of numerous if statements.]

[If the original condition tests FALSE, the first subsequent if else statement is checked. If that also tests FALSE, the next is tested and so on until one conditional statement results in a TRUE result, an else statement is reached, or the end of the conditional block is encountered. In this case, the else statement acts as a “catch all” if none of the else if statements evaluate to TRUE.]

[For example:‡

if (age > 1 && age <= 18) {

MessageBox("Your age is between 1 and 18! You're a kid!");

} else if (age > 18 && age <= 40) {

MessageBox("Your age is between 18 and 40! You're a young adult!");

} else if (age > 40 && age <= 70) {

MessageBox("Your age is between 40 and 70! You're getting up there!");

} else if (age > 70 && age <= 90) {

MessageBox("Your age is between 70 and 90! You're old!");

} else {

MessageBox("Your age is greater than 90! You're really old!");

}

[The if and else if statements are checked sequentially until one is found to be TRUE. If none of them are TRUE, the statements within the else block are executed. Any number of else if conditions can follow an initial if condition; however, only one of them can be executed.]

[Using numerous else if conditions can resemble the action of a switch statement, and often times switch statements are a better choice when comparing the value of a variable to multiple different possible values. For more information on the switch statement, see section 4.10.]

[Each control path must end in a proper return or exit statement.]

 

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GoFiler Legato Script Reference — Generated on 10/21/2024

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