Conditionally execute a statement
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WSupported on Windows
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USupported on Unix
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VSupported on OpenVMS
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NSupported in Synergy .NET
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IF condition statement_1
or
IF condition THEN statement_2 ELSE statement_3
Arguments
condition
An expression whose value controls whether the statement is to be executed.
statement_1
A single or compound statement to be executed if condition is true.
statement_2
A single or compound statement to be executed if condition is true.
statement_3
A single or compound statement to be executed if condition is false.
Discussion
The first form of the IF statement conditionally executes a specified statement.
The second form of the IF statement executes one of two statements based on the value of an expression.
In the first form of the IF statement, if condition is true, statement_1 is executed; if condition is false, statement_1 is skipped. In the second form of the IF statement, if condition is true, statement_2 is executed and statement_3 is skipped; if condition is false, statement_3 is executed and statement_2 is skipped. In all cases, execution continues with the statement following the IF.
Statement_1, statement_2, statement_3 and the THEN and ELSE keywords can each begin on the next logical line.
By default, Synergy DBL requires that an IF statement with a THEN present must also have an ELSE, and the ELSE belongs to the last THEN in the same lexical level.
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You can perform IF tests of the following two forms: if .NOT. dfield if dfield |
Examples
Below is an example of the first form of the IF statement.
clear dflag
display(TTCHN, "Do you want extended screens?")
reads(TTCHN, yesno)
if (yesno .eq. "Y")
xcall ext_scrns
Below is an example of the IF-THEN-ELSE form of the IF statement. In this example, statement1 is processed when answer is equal to Y and choice equals 1, and statement3 is processed when answer is not equal to Y.
if (answer .eq. 'Y') then
if (choice .eq. 1) then
statement1
else
statement2
else
statement3
The following is an example of a cascaded IF statement, which is a series of IF-THEN-ELSE statements that have another IF-THEN-ELSE statement following the ELSE keyword:
if (a_select .eq. 1) then
result = a_v1 + a_v2
else if (a_select .eq. 2) then
result = a_v1 - a_v2
else if (a_select .eq. 3) then
result = a_v1 * a_v2
else if (a_select .eq. 4)
result = a_v1 / a_v2
Although the cascaded IF statement is functionally equivalent to the CASE statement, CASE is more efficient and easier to maintain. See CASE-ENDCASE for more information.
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To avoid logic errors in nested IF statements, do one of the following:
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