1. Chapter 4 Control Structure: Loop Knowledge: Understand the various concepts of loop control structure Skill: Be able to develop a program involving loop control structure 1 Prof. Kuanquan Wang The School of Computer Science and Technology Harbin Institute of technology

2. Outline 4.1 Review and introduction to loop flow control structure 4.2 Loop control with counter 4.3 Loop control with condition test 4.4 Loop control with sentinel

3. 4.1 Review and introduction to loop flow control structure How many basic flow control structure? There are 3 kinds of basic flow control structure. SequenceSelectionRepetition or loop

4. C Programming Language4 C Programming Language 4 How Loops are Controlled? Sentinel Controlled Counter Controlled 1, 2, 3, 4, … …, 4, 3, 2, 1 Condition Controlled

5. C Programming Language5 C Programming Language 5 4.2 Counter Controlled Loop counter ← initial Value test counter value Step n Step x false true Update counter

6. C Programming Language6 C Programming Language 6 Counter Controlled Loop counter = initialValue test counter value Step n Step x false true Update counter counter ← initial Value

7. C Programming Language7 C Programming Language 7 Example: Can you identify the input and output??? Draw a flowchart for the following problem: Read 5 integer and display the value of their summation. Input : 5 integer n1, n2, n3, n4, n5 Output: The summation of n1, n2,.., n5 Input example: 2 3 4 5 6 Output example: 20

8. C Programming Language8 C Programming Language 8 Input n1 Input n2 Input n3 input n4 input n5 output sum sum ← n1+n2+n3+n4+n5 start 2 n1 Assume input example: 2 3 4 5 6 3 n2 4 n3 5 n4 6 n5 20 sum end This flowchart does not use loop, hence we need to use 6 different variables

9. C Programming Language9 C Programming Language 9 Counter- Controlled Loop counter ← 1, sum ← 0 counter < 6 sum ← sum + n false true counter++ output sum input n 1 counter sum 0 1 < 6true 2 n 0 + 2 2 2 2 < 6true 3 2 + 3 5 3 3 < 6true 4 5 + 4 9 4 4 < 6true 5 9 + 5 14 5 5 < 6true 6 14 + 6 20 6 6 < 6false Assume input example: 2 3 4 5 6 This loop is counter-controlled The counter Increases by 1 Uses only 3 variables

10. C Programming Language10 C Programming Language 10 Decreasing Counter-Controlled Loop counter ← 5, sum ← 0 counter > 0 sum←sum+ x false true counter-- output sum input x

11. C Programming Language11 C Programming Language 11 Loop : for Loop : for Condition is tested first Loop is controlled by a counter Syntaxes for (initial value ; condition; update counter) statement; Or for (initial value ; condition; update counter) { statement; }

12. C Programming Language12 C Programming Language 12 i ← 0, sum ← 0 i < 5 sum←sum+ x false true i++ output sum input x int x, sum, i; sum = 0; for (i = 0; i < 5; i++) { scanf(“%d”,&x); sum = sum + x; } printf(“%d”,sum);

13. C Programming Language13 C Programming Language 13 for statement for statement Example: for ( num = 1; num <= 3; num++ ) printf(“%d\t”, num); num ??? _ 1_1_ printf(“have come to exit\n”);

14. C Programming Language14 C Programming Language 14 Example: for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); num 1 _ for statement for statement printf(“have come to exit\n”);

15. C Programming Language15 C Programming Language 15 Example: for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); num 1 _ for statement for statement printf(“have come to exit\n”);

16. C Programming Language16 C Programming Language 16 Example: for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); num 1 1_1_ for statement for statement printf(“have come to exit\n”);

17. C Programming Language17 C Programming Language 17 Example: for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); num 2 1_1_ for statement for statement printf(“have come to exit\n”);

18. C Programming Language18 C Programming Language 18 Example: for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); num 2 1_1_ for statement for statement printf(“have come to exit\n”);

19. C Programming Language19 C Programming Language 19 for statement for statement Example: for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); num 2 12_12_ printf(“have come to exit\n”);

20. C Programming Language20 C Programming Language 20 Example: for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); num 3 12_12_ for statement for statement printf(“have come to exit\n”);

21. C Programming Language21 C Programming Language 21 Example: for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); num 3 12_12_ for statement for statement printf(“have come to exit\n”);

22. C Programming Language22 C Programming Language 22 Example: for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); num 3 123_123_ for statement for statement printf(“have come to exit\n”);

23. C Programming Language23 C Programming Language 23 Example: for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); num 4 123_123_ for statement for statement printf(“have come to exit\n”);

24. C Programming Language24 C Programming Language 24 Example: for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); printf(“have come to exit\n”); num 4 123_123_ for statement for statement

25. C Programming Language25 C Programming Language 25 Example: for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); printf(“have come to exit\n”); num 4 123have come to exit_ for statement for statement

26. C Programming Language26 C Programming Language 26 Loop Structure Condition is tested firstCondition is tested later 4.3 Loop control with condition test

27. C Programming Language27 C Programming Language 27 false true Testing Condition First condition Step x Step y Step a Step n

28. C Programming Language28 C Programming Language 28 Testing Condition First condition Step x Step y Step a Step n

29. C Programming Language29 C Programming Language 29 Loop: while Loop: while  Condition is tested first  Loop is controlled by condition or a counter  Syntax while (condition) statement; Or while (condition) { statement; }

30. C Programming Language30 C Programming Language 30 Step a condition Step n Step x false true Step y Testing condition later

31. C Programming Language31 C Programming Language 31 Step a condition Step n Step x false true Step y Testing condition later

32. C Programming Language32 C Programming Language 32 Do-while Loop Statements in the loop are executed first (at least once), and condition is tested last Loop is controlled by a condition or counter Syntax do { statement; } while (condition); statement;

33. C Programming Language33 C Programming Language 33 Example: Draw a flowchart for this problem; Given an exam marks as input, display the appropriate message based on the rules below:  If marks is greater than 49, display “ PASS ”, otherwise display “ FAIL ”  However, for input outside the 0-100 range, display “ WRONG INPUT ” and prompt the user to input again until a valid input is entered

34. C Programming Language34 C Programming Language 34 Condition-Controlled Loop false true input m m 100 m>49 “PASS” “FAIL” true false “WRONG INPUT” Assume m=110 m 110 110 100 WRONG INPUT Assume m=5 5 5 100 5 > 49 FAIL Assume m=57 57 57 100 57 > 49 PASS Condition-controlled loop with its condition being tested at the end

35. C Programming Language35 C Programming Language 35 false true input m m 100 m>49 “PASS” “FAIL” true false “WRONG INPUT” input m Condition-controlled loop with its condition being tested first

36. C Programming Language36 C Programming Language 36 int marks; scanf(“%d”,&marks); while (marks 100) { printf(“WRONG INPUT”); scanf(“%d”,&marks); } if (marks>49) { printf(“PASS”); else printf(“FAIL”); } Double Selection

37. C Programming Language37 C Programming Language 37 do-while statement Example : printf(“Input start and end value : “); scanf(“%d %d”, &start, &end); do { printf(“%c (%d)\n“, start, start); start++; } while (start <= end) ; _ ??? start ??? end Input start and end value : _Input start and end value : 65 67_ 6567 Input start and end value : 65 67 A (65) _ 66 66 <= 67 Input start and end value : 65 67 A (65) B (66) _ 67 <= 67 67 Input start and end value : 65 67 A (65) B (66) C (67) _ 68 68 <= 67

38. C Programming Language38 C Programming Language 38 4.4 Sentinel-Controlled Loop Draw a flowchart for a problem which: Receive a number of positive integers and display the summation and average of these integers. A negative or zero input indicate the end of input process Can you identify the input and output??? Input: A set of integers ending with a negative integer or a zero Output: Summation and Average of these integers

39. C Programming Language39 C Programming Language 39 Input Example: 30 16 42 -9 Output Example: Sum = 88 Average = 29.33 Sentinel Value

40. C Programming Language40 C Programming Language 40 Now… What have you understand?

41. C Programming Language41 C Programming Language 41 x>0 sum←sum+x false true input x sum←0 input x display sum Try to understand What will happen if this statement is deleted??? ? What happened if these 2 statements exchange places sum←sum+x input x ?

42. C Programming Language42 C Programming Language 42 Exercise Given a set of integers with the last one being 999 Display the summation of all the integers. Input example: 1323999 Output example: Sum = 27 Draw the flowchart for this problem

43. C Programming Language43 C Programming Language 43 Sentinel-controlled loop true x!=999 sum←sum+x false input x sum=0 input x output sum #include void main() { int sum, x; sum = 0; scanf(“%d”, &x); while (x != 999) { sum = sum + x; scanf(“%d”, &x); } printf(“The sum : %d\n”, sum); }

44. C Programming Language44 C Programming Language 44 int sum, x; sum = 0; scanf(“%d”, &x); while (x != 999) { sum = sum + x; scanf(“%d”, &x); } printf(“\nThe sum : %d\n”, sum); ? ? x sum 0 1 _1 1 != 999 0+11 1313 3 3 != 999 1+34 1323 23 23 != 999 4+2327 1323999 999 999 != 999 The sum : 27

45. C Programming Language45 C Programming Language 45 Now… Let us have a summary!  The concept of Loop Structure  3 methods to control loop structure Counter Controlled, Condition Controlled, Sentinel Controlled  3 statements in C language for, while, do while Thank you for your attention! Now let us have a break!