The DO … LOOP is used to repeat a block of statements while a condition is true OR until a condition becomes true.
This type of loop is required when you don’t know how many repetitions you will need before you start.
When you know the number of repetitions,
you use a FOR .. NEXT loop.
There are 5 possible structures for DO Loops
DO WHILE (condition ) DO UNTIL (condition )
Statements Statements
LOOP LOOP
——————————————————————————-
DO DO
Statements Statements
LOOP WHILE (condition ) LOOP UNTIL (condition )
DO
Statements
If ( condition) then exit do
LOOP
In a DO WHILE or LOOP WHILE, the structure will be executed repeatedly, as long as the condition is true. When the condition is no longer true, the compiler will move to the line of code after LOOP.
In a DO UNTIL or LOOP UNTIL, the structure will be executed repeatedly, as long as the condition is not true. When the condition becomes true, the compiler will move to the line of code after LOOP.
When might you use a DO.. LOOP?
A user wants to continue entering numbers and have the computer count how many were entered. Stop when the user enters a “-1”.
Possible Code:
CLS
DIM num AS INTEGER, count as integer
count = 0
DO
INPUT “Please enter a number “, num
count = count + 1
LOOP UNTIL num = -1
count = count – 1 ‘don’t want to include -1 in the count
PRINT USING “You entered ### numbers”; count
———————————————————–
CLS
DIM num AS INTEGER, count as integer
count = 0
INPUT “Please enter a number “, num
DO WHILE num <> -1
count = count + 1
INPUT “Please enter a number ”,num
LOOP
count = count – 1
PRINT USING “You entered ### numbers”; count
———————————————————-
CLS
DIM num AS INTEGER, count as integer
count = 0
DO
INPUT “Please enter a number ”,num
If num = -1 then exit do
count = count + 1
LOOP
PRINT USING “You entered ### numbers”; count
