1. Chapter 7 Problem Solving with Loops
CMPF144 Introduction to Problem Solving and Basic Computer

2. Objectives
Develop problems using loop logic structure with decision and sequential logic structures
Use problem-solving tools (IPO Chart, Pseudocode, Flowchart) when developing solution using loop logic structure
Use counters and accumulators in problem solution

3. Objectives (Cont.)
Distinguish different uses of two types of loop logic structures
Distinguish different uses of two loop designs
Use nested loop instructions to develop problem solution
Use recursion in simple problem

4. Loop Logic Structure Also known as Repetition Control Structure
Is used when we need to perform certain SAME actions REPEATEDLY
Main DIFFICULTY: to identify which instructions should be repeated
Performing TWO (2) standard tasks:
Counting decrementing)
Accumulating ( calculating a total)

5. Loop Logic Structure (Cont.)
Can be categorized into TWO (2) main types:
While/End_While
Repeat/Until
Each type of loop structure has a specific use according to language / problem
Each type of structure DO NOT share the same Pseudocode and Flow chart

6. Counting Can be either INCREMENTING or DECREMENTING
Incrementing is done by adding a constant, such as 1 or 2, to the value of a variable
Example:
Decrementing is a process of subtracting a constant from a current variable’s value
Variable names are the same on both sides of equal sign.
Is a type of assignment instruction
i = i + 1
counter = counter - 2

7. Accumulating A process of summing up a group of numbers
Similar to incrementing, except a variable instead of a constant is added to another variable
Example:
Is also a type of assignment instruction
total = total + number

8. While/End_While Using the keyword of WHILE…THEN….END_WHILE
Tells the computer that while the condition is TRUE, it should repeat ALL instructions between the WHILE and END_WHILE (loop)

9. While/End_While (Cont.)
Diamond is used for the while part, which represents condition / decision
Decision will be checked before executing any instructions within the loop
If resultant is FALSE at the start, the instructions within the loop will NOT be executed
If resultant is TRUE, the complete set of instructions will be executed, and computer will go back to the beginning of the loop and process the condition again, until it is FALSE

10. While/End_While (Cont.)
Pseudocode
Flow Chart
Begin .
WHILE condition(s) THEN
Instruction
END_WHILE
End

11. Exercise 1:
Develop an IPO chart, pseudocode, flowchart and complete Python program, to find the average age of all the students in a class

12. IPO Chart Input Process Output age Get age Calculate average
Display average
average

13. Pseudocode
Begin Set count = 0 Set sum = 0.0 Get age WHILE age <> 0 THEN sum = sum + age count = count + 1 END_WHILE average = sum / count Display average End
Tell me, Which one is:
Primer Read??
Trip flag??

14. Flow Chart Begin Set count = 0 Set sum = 0.0 F T sum = sum + age
Get age
age <> 0 F T
sum = sum + age
count = count + 1
Get age
average = sum/count
Display average
End

15. Python Code
sum = 0.0 count = 0 age = input("How old are you:") while age <> 0: sum = sum + age count = count + 1 average = sum/count print "The average age is", average
Output:

16. Repeat/Until Using the keyword of REPEAT….UNTIL
Tells the computer to repeat the set of instructions between the Repeat and the Until, until a condition is TRUE

17. Repeat/Until (Cont.)
TWO (2) major differences between Repeat/Until loop with While/End_While loop:
In While/End_While loop, program continues to loop as long as resultant of condition is TRUE. Whereas Repeat/Until loop continues to loop while resultant of condition is FALSE
In While/End_While loop, condition is processed at the BEGINNING. However, in the Repeat/Until loop, the condition is processed at the END, which cause the instructions in the loop to be processed at least ONCE, regardless of whether it is necessary (hence, While/End_While is often the preferred choice)

18. Repeat/Until(Cont.) Flow Chart Pseudocode Begin . REPEAT Instruction
UNTIL condition(s)
End

19. Exercise 2: Refer back to same scenario case in Exercise 1
IPO chart is still the same
Pseudocode and Flow chart is different as compared to solution in Exercise 1

20. Pseudocode
Begin Set count = 0 Set sum = 0.0 Get age REPEAT sum = sum + age count = count + 1 UNTIL age == 0 average = sum / count Display average End

21. Flow Chart Begin Set count = 0 Set sum = 0.0 sum = sum + age
Get age
sum = sum + age
count = count + 1
Get age F
age == 0 T
average = sum/count
Display average
End

22. General Design of Loop Two general designs: Automatic-counter loop
Sentinel-controlled loop

23. Automatic-Counter Loop
Also known as counter-controlled loop
Is used when we need to execute a number of instructions from the program for a finite, pre- determined number of time
It increments or decrements a variable (which acts as a counter) each time the loop is repeated

24. Automatic-Counter Loop (Increments)
The programmer uses a variable as a counter that starts counting at a specified number and increments the variable each time the loop is processed.
Example:
The amount to be incremented is specified by the instruction.
The set of instructions within the loop repeats until the counter is greater than an ending number
count = 0
count = count + 2

25. Exercise 3:
Develop an IPO chart, pseudocode, flowchart and complete Python program, to find the average age of FIVE (5) users

26. IPO Chart Input Process Output age Get age Calculate average
Display average
average

27. Pseudocode
Begin Set count = 0 Set sum = 0.0 Get age WHILE count < 4 THEN sum = sum + age count = count + 1 END_WHILE average = sum / count Display average End

28. Flow Chart Begin Set count = 0 Set sum = 0.0 F T sum = sum + age
Get age
count< 4 F T
sum = sum + age
count = count + 1
Get age
average = sum/count
Display average
End

29. Python Code
sum = 0.0 count = 0 age = input(“Your age:") while count < 4: sum = sum + age count = count + 1 average = sum/count print "The average age is", average
Output:

30. Automatic-Counter Loop (Decrements)
The programmer uses a variable as a counter that starts counting at a specified number and increments the variable each time the loop is processed.
Example:
The amount to be decremented is specified by the instruction.
The set of instructions within the loop repeats until the counter is lesser than or not equal to an ending number
count = 10
count = count - 1

31. Exercise 4:
Develop an IPO chart, pseudocode, flowchart and complete Python program, for a program which will prompt for the user to insert a positive integer. The program will then perform count down (decrement by ONE) towards the integer inserted. The message of “Happy New Year” will be displayed AFTER the integer is decreased to ZERO.

32. IPO Chart Input Process Output number Get number
Display number until 0
Display “Happy New Year”
Number
Message of “Happy New Year”

33. Pseudocode
Begin Get number WHILE number >= 0 THEN Display number number = number - 1 END_WHILE Display “Happy New Year” End

34. Display “Happy New Year”
Flow Chart
Begin
Get number F
number >= 0 T
Display number
number = number - 1
Display “Happy New Year”
End

35. Python Code
number=input("Give me a number:") while number >= 0: print number number = number - 1 print "Happy New Year"
Output:

36. Sentinel-controlled Loop
Is used when we need to execute a number of instructions from the program indefinitely until the user tells it to stop or a special condition is met
Indicator (also known as flag, switches, trip values or sentinel values) needs to be set internally in the program to control when the processing of a loop should stop

37. Exercise 5:
Develop an IPO chart, pseudocode, flowchart and complete Python program, for a program which will read in a series of student’s score (as long as the score is not -99). Upon receiving the sentinel value -99, the program will stop reading in students’ score. It will then compute and display average score for all students and the total number of students whom have inserted scores into program.

38. IPO Chart Input Process Output score Get score
Calculate average, count
Display average, count
average
count

39. Pseudocode
Begin Set sum = 0.0 Set count = 0 Get score WHILE score <> -99 THEN sum = sum + score count = count + 1 END_WHILE average = sum / count Display average, count End

40. Flow Chart Begin Set sum = 0.0 Set count = 0 F T sum = sum + score
Get score
score <> -99 F T
sum = sum + score
count = count + 1
Get score
average = sum/count
Display average, count
End

41. Why don’t you try to code??
Python Code
Why don’t you try to code??
Output:

42. Nested Loops Loops can be nested like decision logic structure
Each inner loop must be nested inside the loop just outside it (outer loop)
However, both loops do NOT have to come from the same type of loop structure
Example:
A While/End_While Loop can be nested inside a Repeat/Until Loop

43. Exercise 6:
Develop an IPO chart, pseudocode, flowchart and complete Python program, for a program which will prompt for two inputs from user:
The number of multiplication timetables
The number of rows required in each set of multiplication timetable
The program will then generate a complete timetable set based on user’s requirement

44. IPO Chart Input Process Output number row Get set Get row
Calculate multiply
Display multiply
multiply

45. Begin Get number Get row set i = 1 WHILE i <= number THEN Set j = 1 WHILE j <= row THEN multiply = i * j Display multiply j = j + 1 END_WHILE i = i + 1 Display “*******” End
Pseudocode

46. Flow Chart
It’s drawing time 

47. Sample Output:
Let’s try to code 

48. Recursion Occurs when a module or a function calls back itself
The condition that ends the loop must be within the module
Will be covered in lab module 7

49. More exercises
pp.186, PROBLEMS
Question 1
Question 3

50. Loop Challenges
CONSTRUCT appropriate Pseudocode and Flow chart for each scenario sample output provided
Then CONVERT each Flow chart into complete Python program

51. Loop Challenge - 1

52. Loop Challenge - 2

53. Loop Challenge - 3

54. Loop Challenge - 4
Develop a program to calculate how many years does it take for a user to get RM in his saving account, assuming that he deposited RM5000 into a bank, with yearly interest 2.00%

55. Loop Challenge - 5

56. Loop Challenge - 6

57. Loop Challenge - 7
An applicant for a secretarial job will be given a maximum of five typing tests. The applicant will be hired as soon as he or she scores over 50 words per minute on two tests. Write a program that allows a supervisor to enter each typing test score on completion of each test. The program should print Hire as soon as the applicant qualifies without asking for further tests. If after five test scores have been entered the typist still hasn’t qualified, the program should print reject.

58. Loop Challenge – 7 (cont.)

59. Loop Challenge – 8