The general form for the IF statement is:
IF(logical_expression) simple_statement
For example the statement:
IF(x<0.0) x=-x
makes x positive.
Logical expressions are formed using relational operators and logical operators knowing their order of precedence .
Logical expressions can be stored as LOGICAL variables.
IF statements can be nested within one of the flow control constructs but not vice-versa.
Unlike flow control constructs, an IF statement can not be named.
For most purposes, an IF construct is preferred to an IF statement, even in simple cases. For example,
IF(x<0.0)THEN
x=-x
ENDIF
though less concise, scans more easily. The IF statement may, however, be preferred for use with the statements STOP, RETURN, EXIT and CYCLE.