basic.if

tests the result of a logical expression. Depending on whether the expression evaluates to either 'true' or 'false', the statement(s) following the 'then' or 'else' clauses respectively are executed.

The statements may be placed on a single line (single-line format) or in a block structure (multi-line 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 semicolons.

The single-line format:

if logical.expresssion then statements {else {statements}

where 'statements' represents {statement{; statement{;...}

The single and multiline formats may be combined. Thus, the general format of the multiline statement takes on three forms as shown below:

form 1:

if logical.expresssion then statements else
statements
.
.
end

form 2:

if logical.expresssion then
statements
.
.
end else statements

form 3:

if logical.expresssion then
statements
.
.
end else
statements
.
.
end

form 4:

if logical.expresssion else
statements
.
.
end

form 5:

if logical.expresssion then
statements
.
.
end

If the logical.expresssion evaluates to non-zero, it is considered true. If it evaluates to 0, it is considered false.

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 may be tested by using 'and' and 'or' connectives. No matter how complex the overall expression may be, each condition eventually evaluates to a simple true or false.

Many statements accomodate the 'then/else' construct, and more information is available under the topic, 'then/else construct'.