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

if statement

Syntax

Parameter(s)

Description

Example(s)

See also