is any SAS expression,
enclosed in parentheses. You must specify at least one expression.
The expression is evaluated
at the top of the loop before the statements in the DO loop are executed.
If the expression is true, the DO loop iterates. If the expression
is false the first time it is evaluated, the DO loop does not iterate
There are three other
forms of the DO statement:
The DO statement, the simplest
form of DO-group processing, designates a group of statements to be
executed as a unit, usually as a part of IF-THEN/ELSE statements.
The iterative DO statement executes
statements between DO and END statements repetitively based on the
value of an index variable.
The DO UNTIL statement executes
statements in a DO loop repetitively until a condition is true, checking
the condition after each iteration of the DO loop. The DO WHILE statement
evaluates the condition at the top of the loop; the DO UNTIL statement
evaluates the condition at the bottom of the loop.
Note: If the expression is false,
the statements in a DO WHILE loop do not execute. However, because
the DO UNTIL expression is evaluated at the bottom of the loop, the
statements in the DO UNTIL loop always execute at least once.
Example: Using a DO WHILE Statement
These statements repeat
the loop while N is less than 5. The expression N<5 is evaluated
at the top of the loop. There are five iterations in all (0, 1, 2,