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Objectives Understand Loops

Discuss WHILE loop

Discuss DO. WHILE loop

Discuss the REPEAT . UNTIL loop

Work with the FOR loop

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Loops A loop is a set of statements that are repeated a

certain number of times.

The block of statements written in between theloop gets executed as many number of times as theuser wants

The four types of loops are:

The WHILE loop The DO..WHILE loop The REPEATUNTIL loop The FOR loop

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The While Loop The WHILE loop repeats statements while a

certain specified condition is True

The syntax:

WHILE condition

DO

statement set

END DO

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An ExampleBEGIN

cnt = 0

WHILE (cnt< 1000)DO

DISPLAY Scooby

cnt = cnt+1

END DO

END

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The DOWHILE Loop In the DO WHILE loop the body of the code is executed

once before the test is performed

The general form of the DO WHILE loop isDO

Statements

WHILE conditions

When the condition becomes False in a DO WHILE theloop will be terminated, and the control goes to the

statement that appears immediately after the WHILE

statement.

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An Example

BEGIN

DO

DISPLAY Enter a number

[enter 5 to exit]:

INPUT num

WHILE (num 5)

END

START

DISPLAY "Enter a number [enter 5 to exit]:"

INPUT nu m

num 5

STO P

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The REPEATUNTIL Loop The statements within the loop body get executed

before the condition is evaluated

The loop in the REPEAT.UNTIL loop executesuntil the condition evaluates to true

The general syntax is

REPEAT

Statement-set

UNTIL condition

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An Example

BEGIN

REPEAT

DISPLAY Enter a num [enter 5 to exit]:

INPUT num

UNTIL (num=5)

END

START

DIS PLAY "Enter a num ber [enter 5 to exit]:"

INPUT num

num = 5

S T OP

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The FOR Loop The FOR loop consists of a single line which will include three parts:

Initialization

Condition

Increment / Decrement

The general syntax for a FOR loop is

FORcounterVariable IN RANGEstartvalue to endValue [STEP value]

DO

statement setEND DO

ThestartValue and endValue denote the initial and final values of the counter

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An Example

BEGIN

FOR cnt IN RANGE 1 to 1000

DO

DISPLAY Scooby

END DO

END

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Nested Loops A Nested loop is one loop within another

BEGIN

cnt = 1

cnt2 = 1WHILE cnt < 6

INPUT num

cnt2 = 1

WHILE cnt2 < 3

DO

PRINT numcnt2 = cnt2 + 1

END DO

cnt = cnt + 1

END DO

END

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Breaking out of a Loop To exit from loop, the keyword breakis used

The need to break the loop arises when a search is conducted through a big list. In this case if the

required information is found the first time, then the search need not be continued

BEGIN

DISPLAY To exit type in 999

FOR a IN RANGE 1 to 5

DO

INPUT num

IF num = 999

EXIT LOOP

END IF

DISPLAY num

END DO

END

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Skipping a part of a Loop Skipping certain parts of the loop is done when certain conditions have to be excluded

from the program

BEGINFOR a IN RANGE 1 to 20

DO

IF a= 13

CONTINUE

END IFDISPLAY a

END DO

END