L ecture 11

1. Lecture 11 • Enumeration Type • User-defined Structure • Use of typedef • Readings: Chapter 7 Section 1-5, Chapter 12 Section 1-7

2. Enumeration Types • Allows us to name a finite set and to declare identifiers, called enumerators, for the elements of the set • Declaration: enum day {sun, mon, tue, wed, thu, fri, sat}; • This creates the user-defined typeenum day • The keyword enum is followed by the tag name day • The enumerators are the identifiers sun, mon,…,sat. They are constant of type int • The value of first enumerator is 0, and each succeeding one has the next integer value i.e.,sun = 0, mon = 1, tue = 2,….,sat = 6 • To declare a new variable with enumeration type: enum day d1;

3. Enumeration Type (con’t) • Declare multiple variables: enum day d1, d2; • This declares d1 and d2to be of type enum day • The variables can take on as values only the elements (enumerators) in the set Example: d1 = fri; d2 = wed; • Test whether d1 is equal to d2: if (d1 == d2)

4. Enumeration Type • Initialize enumerators enum suit {clubs = 1, diamonds, hearts, spades}; • clubsis initialized to1, diamonds, hearts, spades have the values of 2, 3, 4 enum fruit {apple = 7, pear, orange = 3, lemon}; • pear has value 8, lemon has value 4 • Multiple values are allowed, but the enumerators themselves must be unique • Initialize enumerators and declare variables: enum suit { clubs=1, diamonds, hearts, spades} a, b, c;

5. The use of typedef • C provides the typedef facility so that an identifier can be associated with a specific type: • Example: typedef int color; • This makes color a type that is synonymous with int • color can be used to declare variables: color c1, c2; /* c1 and c2 are variables of type color */ • Use typedeffor enumeration type: enum day {sun, mon, tue, wed, thu, fri, sat}; typedef enum day day; day next_day;

6. Example /* Compute the next day */ enum day {sun, mon, tue, wed, thu, fri, sat}; typedef enum day day; day find_next_day(day d) { day next_day; switch (d) { case sun: next_day = mon; break; case mon: next_day = tue; break; ... case sat: next_day = sun; } return next_day; }

7. Programming Style • Use of enumeration types is considered a good programming style!!! • Example: Rather than use 0 and 1 to distinguish between alternate choices, a programmer can easily use an enumeration type enum bool {false, true}; enum on_off {off, on}; enum yes_no {no, yes}; • Can further use typedef: typedef enum veg {beet, carrot, corn} veg; OR typedef enum {beet, carrot, corn} veg;

8. Common Programming Error #include <stdio.h> typedef enum {yes, no} yes_no; yes_no is_good(); void main(){ if (is_good()) printf(“Hooray! A good condition exists!\n”); else printf(“Rats! Another bummer\n”); } yes_no is_good() { ……………… /* return yes if good, otherwise return no */ } • Be careful! The order in which you define enumerators can easily lead to logical errors.

9. User defined structures • Allows the user to create a container for a collection of data items having different types • Format: Creation of a user-defined structure structtag_name{ data_typevariable1; data_type variable2; ... }; Declare variable with this user defined structure: structtag_namevariable_name;

10. Variations – create and declare Creation of user defined structure Variable declaration

11. With user defined structure - structure.c • A structure is a container storing a number of variables • Use a structure to define a card (card type, number) A new user defined structure - card Associate card with structcard

12. This function returns a structure that contains two members. Variable declaration Use the variable face within the card random with the dot (structure member operator)

13. The complete program #include <stdio.h> #include <stdlib.h> #include <time.h> typedef enum cardtype {diamond=1, club, heart, spade} cardtype; typedef enum {false, true} boolean; struct card { cardtype face; int num; }; typedef struct card card; card getAcard() /* generate a card with a type and number */ { card random; random.face = rand()%4+1; random.num = rand()%13+1; return random; }

14. boolean greater(card c1, card c2) { if (c1.num > c2.num) return true; else if (c1.num < c2.num) return false; else { if (c1.face > c2.face) return true; else return false; } }

15. void printCard(card c) { switch (c.face) { case diamond: printf(“Diamond “); break; case club: printf(“Club “); break; case heart: printf(“Heart “); break; case spade: printf(“Spade “); break; } switch (c.num) { case 11: printf(“J\n”); break; case 12: printf(“Q\n”); break; case 13: printf(“K\n”); break; case 1: printf(“A\n”); break; default: printf(“%d\n”, c.num); /* c.num is 2-10 */ } }

16. void main() { card myCard, yourCard; srand((unsigned) time(NULL)); /* init. Random generator */ myCard = getAcard(); printf(“My card is:\t”); printCard(myCard); yourCard = getAcard(); printf(“Your card is:\t”); printCard(yourCard); if (greater(myCard, yourCard)) printf(“My card is greater than your card\n”); else if (greater(yourCard, myCard)) printf(“Your card is greater than my card\n”); else printf(“The two cards are the same\n”); }

17. Another example – structure2.c • Modify the previous program to: • Pick 5 cards from the pile, and find out all the pairs • Modifications: • An array (pile) to store a pile of cards • A variable (nr_left) to keep track of no. of remaining cards • A function (initPile) to initialize the pile of cards • A function (pickAcard) to pick one card from the pile • A function (pair) to check if 2 cards is a pair

18. card pile[52]; int nr_left; void initPile() { int i; for (i=0; i<52; i++) { pile[i].face = (i/13)+1; pile[i].num = (i%13)+1; } nr_left=52; } card pickAcard() { card random; int i; i = rand()%nr_left; random = pile[i]; pile[i] = pile[nr_left-1]; nr_left--; return random; }

19. boolean pair(card c1, card c2) { if (c1.num == c2.num) return true; else return false; } void main() { card myCard[5]; int i, j; srand((unsigned) time(NULL)); /* init. random generator */ initPile(); printf(“My cards are:\n”); for (i=0; i<5; i++) { myCard[i] = pickAcard(); printf(“%2d: “, i); printCard(myCard[i]); } for (i=0; i<4; i++) for (j=i+1; j<5; j++) if (pair(myCard[i], myCard[j])==true) printf(“Card %d and %d is a pair\n”, i, j); }