Eltham High School
Information Technology
Problem Solving and Program Design
LOOP
This is also known as ITERATION/REPETITION. A loop happens when on e or more
programming instructions are repeated until a condition is met. There are three major types of
loops:
 FOR----DO
 WHILE and WHILE----DO
 REPAET ---UNTIL
The above types of loop can be categorized as BOUNDED OR UNBOUND LOOPS.
Bounded Loop (Definite Loop):
This type of loop is set to repeat a process a number of times. With this loop, you know
where you are starting until you end. So the loop as a start and an end that you are aware of.
 FOR---DO
FOR---DO LOOP STRUCTURE
FOR counter = <start number> TO <end number> DO
<Statement 1>
<Statement 2>
ENDFOR
Example:
Write a pseudocode to print, “This is a loop” 5 times on the screen.
FOR counter = 1 TO 5 DO
Print “This is a loop”
ENDFOR
The above loop will be printed/run five (5) times with the result below
1. This is a loop
2. This is a loop
3. This is a loop
4. This is a loop
5. This is a loop
At the end of writing it 5 times, the loop will stop because it reach the limit.
**ACTIVITIES**
Write a for loop to print the following.
1. To print the words “this is a loop 3 times.
2. Ge the name of 4 people and their age.
3. Get the age of 5 people.
4. Get 6 test scores.
5. Get 4 test score and add them.
1
UNBOUNDED LOOP (INDEFINITE LOOP):
This type of loop repeats a set of steps or instructions until a particular condition becomes
false. It allows a program to be repeated multiple times, just as when you let a song repeats
multiple times.
 WHILE and WHILE---DO
 REPEAT---UNTIL
WHILE STRUCTURE
With this type of loop it will check to see if the condition is TRUE and while the condition is
TRUE it will repeat the code until it is no true/false. This type of loop is also called a TOP
CHECKING LOOP as the control condition is placed at the first line of the code. If the
statement/instruction encloses in the loop are false the loop will never be executed. This is
also similar to he IF statement.
It check the condition before entering the loop.
WHILE < condition>
<statement/instruction>
ENDWHILE
Examples:
Write a pseudodoce to let persons get a ride while they have more than 0 tickets.
While x < 8
Print x
X = x+1
The above loop will print
Say the value enter for x at first is 4 then it will be,
Print 4
Then add 1 to that 4: x = x+1
Print 5
Then add 1 to that 5: x = x + 1
Print 6
Then add 1 to that 6: x = x + 1
Print 7
Then add 1 to that 7: x = x + 1
Print 8
At this point 8 is not less than 8 so that means you are done with the while loop and it
becomes false.
**ACTIVITIES**
Write loop for the following.
1. Print the numbers from 0 to 4
2. Print the numbers from 1 to 5
3. Find the sum of 10 and 1 while sum is not equal to 14.
2
WHILE---DO LOOP STRUCTURE
This type of loop is similar to a while loop only difference is that the while do loop condition
is tested at the end of the loop. Therefore, the instruction/statement is executed at least once
before the condition is tested. It is also called the BOTTOM-CHECKING LOOP
WHILE <condition is true> DO
<Instruction 1>
<Instruction 2>
<Instruction 3>
ENDWHILE
Example:
Input a number that is less than 6.
Print “enter a number less than 6”
Read num
WHILE num < 6 DO
Print “that is not less than 6”
Read num
ENDWHILE
If the user had entered 2 that means you can now repeat the action of entering numbers until 6
or a number that is greater than 6 is entered.
**ACTIVITIES**
Write a while do loop for the following.
1. Write a pseudocode to get numbers until 0 is entered.
2. Write a while loop to collect series of numbers and only stop when the user enters 999
3. Write a while loop to collect names and stop when the user enters x.
4. Write a while loop to collect numbers from users and stop when the user enter a
number that is less than 7.
3
REPEAT---UNTIL LOOP STRUCTURE
This loop executes a block statement (s) repeatedly, until a given condition evaluates to
TRUE. This loop test the condition at the bottom of the loop. It is a bit similar to the WHILE
loop EXCEPT that the REPEAT UNTIL loop is guaranteed to execute at least one time.
REPEAT
<instruction 1/statement 1>
<instruction 2/statement 2>
<instruction 3/statement 3>
UNTIL <condition is met>
Examples:
Pseudocode to determine adult age.
REPEAT
Read age
UNTIL age >= 18
**ACTIVITIES**
Write a repeat until loop for the following.
1. To collect a series of numbers and only stop when the user enters 999.
2. Collect names form user and stop if the user enters an x.
3. Collect ages and name and stop when they enter an age over 18.
LOOPS FLOWCHART
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