Control Structure: Loop

Transcription

1 Control Structure: Loop Knowledge: Understand the various concepts of loop control structure Skill: Be able to develop a program involving loop control structure 1

2 Loop Structure Condition is tested first Condition is tested later TK1913-C Programming 2

3 Testing Condition First Step a condition false true Step x Step y Step n TK1913-C Programming 3

4 Testing Condition First Step a condition Step x Step y Step n TK1913-C Programming 4

5 Testing condition later Step a Step x Step y true condition false Step n TK1913-C Programming 5

6 Testing condition later Step a Step x Step y true condition false Step n TK1913-C Programming 6

7 How Loops are Controlled Condition Controlled Counter Controlled 1, 2, 3, 4,, 4, 3, 2, 1 Sentinel Controlled TK1913-C Programming 7

8 Counter Controlled Loop counter initialvalue true test counter value Step x false Update counter Step n TK1913-C Programming 8

9 Counter Controlled Loop counter = initialvalue true test counter value Step x false Update counter Step n TK1913-C Programming 9

10 Example: Draw a flowchart for the following problem: Read 5 integer and display the value of their summation. Can you identify the input and output??? Input : 5 integer n1, n2, n3, n4, n5 Output: The summation of n1, n2,.., n5 Input example: Output example: 20 TK1913-C Programming 10

11 Assume input example: start Input n1 n1 2 This flowchart does not use loop, hence we need to use 6 different variables Input n2 Input n3 input n4 n2 n3 n input n5 n5 6 sum n1+n2+n3+n4+n5 sum 20 output sum end TK1913-C Programming 11

12 Counter- Assume input Controlled example: Loop counter 1, sum 0 false counter < 6 true counter sum < < 6 6 false true input n n sum sum + n counter++ output sum The Uses This counter loop only is counter-controlled Increases 3 variables by 1 TK1913-C Programming 12

13 Decreasing Counter-Controlled Loop counter 5, sum 0 true counter > 0 input x sum sum+ x false counter-- output sum TK1913-C Programming 13

14 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 range, display WRONG INPUT and prompt the user to input again until a valid input is entered TK1913-C Programming 14

15 Condition-Controlled Loop Assume m=110 m=57 m input m WRONG INPUT < < 0 < > >100 >100 true m<0 m>100 false 5 > Condition-controlled > 49 loop with its condition being tested at the end false m>49 PASS FAIL true WRONG FAIL PASS INPUT TK1913-C Programming 15

16 input m m<0 m>100 true WRONG INPUT false input m Condition-controlled loop with its condition being tested first false m>49 PASS FAIL true TK1913-C Programming 16

17 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 TK1913-C Programming 17

18 Input Example: Sentinel Value Output Example: Sum = 88 Average = TK1913-C Programming 18

19 Now What have you understand? TK1913-C Programming 19

20 Try to understand sum 0 input x x>0 true sum sum+x input x false What will happen? if this statement is deleted??? What happened if these 2 statements exchange places sum sum+x input x display sum? TK1913-C Programming 20

21 for while do-while TK1913-C Programming 21

22 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; statement; } TK1913-C Programming 22

23 Example Write a program which does the following: Reads 5 integers and displays the sum of all integers Input example: Output example: 16 TK1913-C Programming 23

24 Recall the flowchart counter 1, sum 0 true counter < 6 input x sum sum+ x false counter++ output sum TK1913-C Programming 24

25 Note the initial value of i and condition How many times does the loop get executed? i 1, sum 0 true i < 6 input x sum sum+ x i++ false output sum TK1913-C Programming 25

26 i 0, sum 0 How many times does the loop get executed? true i < 6 input x sum sum+ x i++ output sum false TK1913-C Programming 26

27 i 0, sum 0 How many times does the loop get executed? true i < 5 input x sum sum+ x i++ output sum false TK1913-C Programming 27

28 The C statements: int x, sum, i; sum = 0; for (i = 0; i < 5; i++) { scanf( %d,&x); sum = sum + x; } printf( %d,sum); TK1913-C Programming 28

29 i 0, sum 0 true i < 5 input x sum sum+ x i++ output sum false int x, sum, i; sum = 0; for (i = 0; i < 5; i++) { scanf( %d,&x); sum = sum + x; } printf( %d,sum); TK1913-C Programming 29

30 for statement Example: for ( num = 1; num <= 3; num++ ) printf( %d\t, num);??? num 1 TK1913-C Programming 30

31 for statement Example: for (num = 1; num <= 3; num++ ) printf( %d\t, num); 1 num _ TK1913-C Programming 31

32 for statement Example: for (num = 1; num <= 3; num++ ) printf( %d\t, num); 1 num _ TK1913-C Programming 32

33 for statement Example: for (num = 1; num <= 3; num++ ) printf( %d\t, num); 1 num 1 _ TK1913-C Programming 33

34 for statement Example: for (num = 1; num <= 3; num++ ) printf( %d\t, num); 2 num 1 _ TK1913-C Programming 34

35 for statement Example: for (num = 1; num <= 3; num++ ) printf( %d\t, num); 2 num 1 _ TK1913-C Programming 35

36 for statement Example: for (num = 1; num <= 3; num++ ) printf( %d\t, num); 2 bil 1 2 _ TK1913-C Programming 36

37 for statement Example: for (num = 1; num <= 3; num++ ) printf( %d\t, num); 3 num 1 2 _ TK1913-C Programming 37

38 for statement Example: for (num = 1; num <= 3; num++ ) printf( %d\t, num); 3 num 1 2 _ TK1913-C Programming 38

39 for statement Example: for (num = 1; num <= 3; num++ ) printf( %d\t, num); 3 num _ TK1913-C Programming 39

40 for statement Example: for (num = 1; num <= 3; num++ ) printf( %d\t, num); 4 num _ TK1913-C Programming 40

41 for statement Example: for (num = 1; num <= 3; num++ ) printf( %d\t, num); 4 num _ TK1913-C Programming 41

42 for while do-while TK1913-C Programming 42

43 Loop: while Condition is tested first Loop is controlled by condition or a counter Syntax while (condition) statement; Or while (condition) { statement; statement; } TK1913-C Programming 43

44 Recall this example: 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 range, display WRONG INPUT and prompt the user to input again until a valid input is entered TK1913-C Programming 44

45 input m m<0 m>100 true WRONG INPUT false Exercise: Convert this flowchart to a C program input m false m>49 PASS FAIL true TK1913-C Programming 45

46 int marks; scanf( %d,&marks); while (marks<0) (marks>100) { printf( WRONG INPUT ); scanf( %d,&marks); } if (marks>49) { printf( PASS ); else printf( FAIL ); } Double Selection TK1913-C Programming 46

47 Exercise Given a set of integers with the last one being 999 Display the summation of all the integers. Input example: Draw the flowchart for this problem Output example: Sum = 27 TK1913-C Programming 47

48 Sentinel-controlled loop sum=0 input x x!=999 sum sum+x input x output sum false true #include <stdio.h> 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); } TK1913-C Programming 48

49 int sum, x; sum = 0; scanf( %d, &x); while (x!= 999) { sum = sum + x; scanf( %d, &x); !=!= 999!= 999 } printf( \nthe sum : %d\n, sum); x ? sum ? _ The sum : 27 TK1913-C Programming 49

50 Do-while Loop Statements in the loop are executed first (at least onc, and condition is tested last Loop is controlled by a condition or counter Syntax do { statement; statement; } while (condition); statement; TK1913-C Programming 50

51 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) ; <= 67 _ Input start and end value : _ 65 67_ A (65) _ B (66) _ C (67) _??? ??? 67 start end TK1913-C Programming 51

52 _ 0 is an even number._ Print iff even! continue statement _ 2 is an even number._ Print iff even! _ 4 is an even number._ Print iff even! Example: _ for ( i = 0; i <= 5; i++ ) { if ( i % 2 ) continue; else printf( %d is an even number., i); printf( Print iff even! \n ); } i i <= 5 i % <= 5 <= 59 false 5 true 10 TK1913-C Programming 52

53 Now what can you conclude about continue? TK1913-C Programming 53

54 break statement Input a value between 1-7: _ YeePee! I m out of the loop! printf( Input a value between 1 7: ); scanf( %d,&value); for (i = 1; i <= 7; i++) { if ( i = = value ) break; printf( \n%d,i); } printf( YeePee! I m out of the loop!\n );??? 4 value i i <= 7 i == value <= <= 7 7 true == 4 false true TK1913-C Programming 54

55 Now what can you conclude about break? TK1913-C Programming 55

56 End of 1 st half of the semester Yes!! That s all? What s next??? Procedure & Function TK1913-C Programming 56