C Programming. Lecture no. 2 More on Control Statements

Transcription

1 C Programming Lecture no. 2 More on Control Statements

2 คำส งในกำรควบค มโปรแกรม 2

3 คำส ง if อย ำงง ำย ค ำส ง if เป นค ำส งสำหร บกำร สร ำงสำยกำรควบค มกำรท ำงำน ออกเป น 2 สำย ร ปแบบ if (condition) statement; Ex: if (height >= 180) { printf( You are very Tall\n ); 3

4 คำส ง if / คำส งเง อนไข if... ร ปแบบ if <condition> statement1; statement2; condition = เง อนไขในการต ดส นใจ statement = คาส งหร อกล มคาส ง ต วอย ำง if (score>80) printf ( Excellent ); printf ( Good ); 4

5 Flow Chart ของคำส งเง อนไข Yes Condition No Statement 1 Statement 2 5

6 Activity Break if (x == 0.0) printf ("x is equal to 0.\n"); y = 0; printf ("x is greater or less than 0.\n"); y = 1; 6

7 Activity Break if (x == 0.0) { printf("x is equal to 0.\n"); y = 0; printf("x is greater or less than 0.\n"); y = 1; 7

8 Activity Break if (x == 0.0) { printf("x is equal to 0.\n"); y = 0; { printf("x is greater or less than 0.\n"); y = 1; 8

9 คำส ง if / หลำยทำงเล อก คำส งเง อนไข if... if ร ปแบบ if <condition1> statement1; if <condition2> statement2; statement3; ต วอย ำง 0 <= x <= 69 : Standard 70 <= x <= 79 : Good x >= 80 : Very Good if (score >= 80) printf ( Very Good ); if (score >= 70) printf ( Good ); printf ( Standard ); 9

10 If-then- a review Let s start out by reviewing what we know about the ifthen- statement 10

11 if statement if (Age < 18) { printf( A child!\n ); 11

12 if- statement if (Age < 18) { printf( A child!\n ); { printf( An adult!\n ); 12

13 if--if statement if (Age < 13) { printf( A child!\n ); if ((Age >= 13 ) && (Age <= 17)) { printf( A teenager!\n ); { printf( An adult!\n ); 13

14 Braces { if (Age < 13) printf( A child!\n ); if ((Age >= 13 ) && (Age <= 17)) printf( A teenager!\n ); printf( An adult!\n ); Not required if branch has only one statement. We recommend you always use braces in this course. Sometimes we omit them to fit our examples on a slide. 14

15 Nested if/ if (Gender == M ) if (Age < 18) printf( A male child!\n ); printf( A man!\n ); if (Age < 18) printf( A female child!\n ); printf( A woman!\n ); Nested if/ is different from if--if... 15

16 Nested if/ vs if-then--if Age < 13 Age >= 13 && child Age <= 17 teenager Age > 17 adult Age < 18 Gender = M Age < 18 male child man female child woman 16

17 Activity Can our nested if/ example be re-code as an if-then-if? If so, do so! If so, can a nested if/ always be re-coded as an if-then-if? If so, why not always use if-then--if instead of a nested if/? 17

18 Activity Break 18

19 Activity Feedback if ((Gender == M ) && (Age < 18)) printf( A male child!\n ); if (Gender == M ) printf( A man!\n ); if (Age < 18) printf( A female child!\n ); printf( A woman!\n ); 19

20 Activity Feedback Nested if/ can always be re-coded as an if-then--if. We do not always use if-then--if instead of a nested if/ because: conditions become more complicated we may wish to perform some common processing for all cases in a sub-branch 20

21 Activity Feedback if (Gender == M ) { NbrMales = NbrMales + 1; if (Age < 18) printf( A male child!\n ); printf( A man!\n ); { : 21

22 Handling other cases One must always be aware of the need to handle other cases.. What are the cases that we are expected to be able to handle? Do we need to consider the possibility of encountering other cases? If so, how should we handle them? 22

23 Nested if/ if (Gender == M ) if (Age < 18) printf( A male child!\n ); printf( A man!\n ); if (Gender == F ) if (Age < 18) printf( A female child!\n ); printf( A woman!\n ); printf( Unknown gender!\n ); 23

24 Activity (เง อนไขท ไม จำเป น) if (x < 0.0) { range = 0; if (x >= 0.0 && x < 10.0) { range = 1; if (x >= 10.0 && x < 100.0) { range = 2; range = 3; if (x < 0.0) { range = 0; if (x < 10.0) { range = 1; if (x < 100.0) { range = 2; range = 3; 24

25 คำส ง switch คำส งเง อนไข Switch ร ปแบบ switch(variable) { case constant1: statement1; break; case constant2: statement2; break; variable = ต วแปร หร อ น พจน constant = ค าคงท ชน ด int หร อ char ท เป นต วเล อกทางาน 25

26 Flow Chart ของคำส งแบบหลำยเง อนไข Condition 1 Yes Statement 1 No Condition 2 Yes No Condition 3 No Statement 2 Yes Statement 3 Statement 4 26

27 If--if if (day == 1) printf ("Sunday\n"); if (day == 2) printf ("Monday\n"); if (day == 3) printf ("Tuesday\n"); if (day ==4) printf ("Wednesday\n"); if (day ==5) printf ("Thursday\n"); if (day ==6) printf ("Friday\n"); if (day ==7) printf ("Saturday\n"); printf ("Unknown\n") switch (expression) { case constant1 : statement_sequence1 break; case constant2 : statement_sequence2 break;... case constantn : statement_sequencen break; default : statement_sequencen+1 27

28 If--if and Switch if (day == 1) printf ("Sunday\n"); if (day == 2) printf ("Monday\n"); if (day == 3) printf ("Tuesday\n"); if (day ==4) printf ("Wednesday\n"); if (day ==5) printf ("Thursday\n"); if (day ==6) printf ("Friday\n"); if (day ==7) printf ("Saturday\n"); printf ("Unknown\n") switch (day) { case 1 : printf ("Sunday\n"); break; case 2 : printf ("Monday\n"); break; case 3 : printf ("Tuesday\n"); break; case 4 : printf ("Wednesday\n"); break; case 5 : printf ("Thursday\n"); break; case 6 : printf ("Friday\n"); break; case 7 : printf ("Saturday\n"); break; default : printf ("Unknown option! \n"); 28

29 Activity switch (digit) { case 2: case 3: case 5: case 7: printf("%d is a prime number.\n", digit); break; default: if (digit >= 0 && digit <= 9) printf("%d is not a prime number.\n", digit); printf("invalid option: %d\n", digit); 29

30 END