Iterations
Iterative statements repeat the associated statements until a specified condition becomes FALSE.
WHILE statement
This statement has the following form:
WHILE expression
statement(s)
ENDWHILE
The expression is evaluated. If the result is TRUE (that is, non-zero), the statements between WHILE and ENDWHILE are executed. The process is then repeated until the expression is FALSE (that is, zero). When the expression evaluates to FALSE, control passes to the statement after ENDWHILE. For example:
LONG counter
counter = 1
WHILE counter <= 10000
counter = counter + 1
ENDWHILE
FOR statement
This statement has the following form:
FOR num_var = num_expr_1 TO num_expr_2 [STEP num_expr_3]
statement(s)
ENDFOR
The num_var variable is referred to as the loop variable. Num_expr_1 specifies the initialization of the loop variable. Num_expr_2 specifies the end value of the loop variable. Num_expr_3 specifies the step size for each iteration. The latter variable is optional; the default step size is 1. It is possible to use a negative step size.
After execution of the statements within the loop, num_expr_3 is added to the loop variable. The num_expr_2 expression is then evaluated. If the loop variable does not exceed num_expr_2, the statements are executed again. This process continues until the loop variable exceeds its end value. For example:
LONG total, i
FOR i = 1 TO 100 STEP 2
total = total + i
ENDFOR
REPEAT ... UNTIL statement
The REPEAT ... UNTIL differs from the WHILE statement, in that the REPEAT ... UNTIL statement tests the condition after execution of the loop statements instead of before execution of the loop statements. Consequently the statement(s) within a REPEAT ... UNTIL statements are executed at least once.
The syntax of this statement is:
REPEAT
statement(s)
UNTIL expression
The loop iterates until the result of the expression becomes non-zero.
Using BREAK and CONTINUE (iterations)
You can use the BREAK command in an iterative statement in order to cancel the loop, regardless of the value of the loop condition. After a BREAK, control passes to the statement following the terminated loop. It is important to note that with nested loops the BREAK statement cancels the innermost loop only.
The CONTINUE command also interrupts an iteration loop. But, in this case, the expression is immediately evaluated again for the next iteration. For example:
LONG numbers(100), i
FOR i = 1 TO 100
IF numbers(i) <= 0 THEN
CONTINUE | Next iteration
ENDIF
IF NOT process(numbers(i)) THEN
BREAK | Exit FOR statement
ENDIF
ENDFOR
The BREAK and CONTINUE commands can be very useful in a program, but you should be take great care when using them.
Related topics
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