if Statement

The if statement tests the result of a logical expression. Depending on whether the expression evaluates to either true or false, the statements following the then or else clauses respectively are executed.

Syntax

The single-line format:

if logical.exp then statement.block

if logical.exp else statement.block

if logical.exp then statement.block else statement.block

The multi-line format:

Form 1:

if logical.exp then statements else

statements

.

.

end

Form 2:

if logical.exp then

statements

.

.

end else statements

Form 3:

if logical.exp then

statements

.

.

end else

statements

.

.end

Form 4:

if logical.exp else

statements

.

.

end

Form 5:

if logical.exp then

statements

.

.

end

Parameter(s)

logical.exp

Expression to be tested. If it evaluates to nonzero, it is considered true. If it evaluates to 0, it is false.

then statement.block

Executes the specified statements if the logical expression evaluates to nonzero.

else statement.block  

Executes the specified statements if the logical expression evaluates to 0.

Description

Commands can be placed on a single line (single-line format) or in a block structure (multiline format). The two formats are functionally identical.

If more than one statement is contained in either the then or else clause, they must be separated by a semicolon.

The single and multiline formats can be combined.

If there is no clause for the current condition, the next sequential statement following the entire if statement is executed.

The then clause of an if statement is optional if the else clause is present. However, one or the both must be present.

Complex conditions can be tested by using the and and or connectives. Regardless of the complexity of the overall expression, each condition eventually evaluates to a simple true or false.

Many statements accommodate the then/else construct. More information is available under the topic, then/else Statement Blocks.

Example(s)

if answer = ’exit’ then stop

if answer = ’y’ then print ’ok’; cnt=cnt+1; goto 20

if answer = ’y’ then

print ’ok’

cnt=cnt+1

end

if answer = ’exit’ then gosub 100 else gosub 200

if answer = ’y’ then print ’ok’;cnt=cnt+1 else print ’no good’;stop

if answer = ’y’ then

print ’ok’

cnt=cnt+1

end else

print ’no good’

end

See Also

! Logical Operator

= Assignment Operator

Boolean Evaluation

Branching

case Statement

else Clause

ifr Statement

Logical Expressions

match Relational Operator

not() Function

null Statement

open Statement

readnext Statement

rewind Statement

Statement Blocks

Statements and Functions

then/else Statement Blocks

writet Statement