structure

Outline
Introduction
Structure Definitions
Initializing Structures
Accessing Members of Structures
Using Structures with Functions
Typedef
Example: High-Performance Card Shuffling and
Dealing Simulation
Unions

 Structures
◦ Collections of related variables (aggregates) under one
name
 Can contain variables of different data types
◦ Commonly used to define records to be stored in files
◦ Combined with pointers, can create linked lists, stacks,
queues, and trees

 Example
struct card {
char *face;
char *suit;
};
◦ struct introduces the definition for structure card
◦ card is the structure name and is used to declare
variables of the structure type
◦ card contains two members of type char * -
face and suit

 Struct information
◦ A struct cannot contain an instance of itself
◦ Can contain a member that is a pointer to the same
structure type
◦ Structure definition does not reserve space in memory
◦ Creates a new data type that used to declare structure
variables.
 Declarations
◦ Declared like other variables:
card oneCard, deck[ 52 ], *cPtr;
◦ Can use a comma separated list:
struct card {
char *face;
char *suit;
} oneCard, deck[ 52 ], *cPtr;

 Valid Operations
◦ Assigning a structure to a structure of the same type
◦ Taking the address (&) of a structure
◦ Accessing the members of a structure
◦ Using the sizeof operator to determine the size of a
structure

 Initializer lists
◦ Example:
card oneCard = { "Three", "Hearts" };
 Assignment statements
◦ Example:
card threeHearts = oneCard;
◦ Or:
card threeHearts;
threeHearts.face = “Three”;
threeHearts.suit = “Hearts”;

 Accessing structure members
◦ Dot operator (.) - use with structure variable name
card myCard;
printf( "%s", myCard.suit );
◦ Arrow operator (->) - use with pointers to structure
variables
card *myCardPtr = &myCard;
printf( "%s", myCardPtr->suit );
myCardPtr->suit equivalent to
( *myCardPtr ).suit

 Passing structures to functions
◦ Pass entire structure
 Or, pass individual members
◦ Both pass call by value
 To pass structures call-by-reference
◦ Pass its address
◦ Pass reference to it
 To pass arrays call-by-value
◦ Create a structure with the array as a member
◦ Pass the structure

 typedef
◦ Creates synonyms (aliases) for previously defined
data types
◦ Use typedef to create shorter type names.
◦ Example:
typedef Card *CardPtr;
◦ Defines a new type name CardPtr as a synonym for type
Card *
◦ typedef does not create a new data type
 Only creates an alias

 Pseudocode:
◦ Create an array of card structures
◦ Put cards in the deck
◦ Shuffle the deck
◦ Deal the cards

1. Load headers
1.1 Define struct
1.2 Function
prototypes
1.3 Initialize deck[]
and face[]
1.4 Initialize suit[]
1 /* Fig. 10.3: fig10_03.c
2 The card shuffling and dealing program using structures */
3 #include <stdio.h>
4 #include <stdlib.h>
5 #include <time.h>
6
7 struct card {
8 const char *face;
9 const char *suit;
10 };
11
12 typedef struct card Card;
13
14 void fillDeck( Card * const, const char *[],
15 const char *[] );
16 void shuffle( Card * const );
17 void deal( const Card * const );
18
19 int main()
20 {
21 Card deck[ 52 ];
22 const char *face[] = { "Ace", "Deuce", "Three",
23 "Four", "Five",
24 "Six", "Seven", "Eight",
25 "Nine", "Ten",
26 "Jack", "Queen", "King"};
27 const char *suit[] = { "Hearts", "Diamonds",
28 "Clubs", "Spades"};
29
30 srand( time( NULL ) );

2. Randomize
2. fillDeck
2.1 shuffle
2.2 deal
3. Function definitions
31
32 fillDeck( deck, face, suit );
33 shuffle( deck );
34 deal( deck );
35 return 0;
36 }
37
38 void fillDeck( Card * const wDeck, const char * wFace[],
39 const char * wSuit[] )
40 {
41 int i;
42
43 for ( i = 0; i <= 51; i++ ) {
44 wDeck[ i ].face = wFace[ i % 13 ];
45 wDeck[ i ].suit = wSuit[ i / 13 ];
46 }
47 }
48
49 void shuffle( Card * const wDeck )
50 {
51 int i, j;
52 Card temp;
53
54 for ( i = 0; i <= 51; i++ ) {
55 j = rand() % 52;
56 temp = wDeck[ i ];
57 wDeck[ i ] = wDeck[ j ];
58 wDeck[ j ] = temp;
59 }
60 }
Put all 52 cards in the deck.
face and suit determined by
remainder (modulus).
Select random number between 0 and 51.
Swap element i with that element.

3. Function definitions
61
62 void deal( const Card * const wDeck )
63 {
64 int i;
65
66 for ( i = 0; i <= 51; i++ )
67 printf( "%5s of %-8s%c", wDeck[ i ].face,
68 wDeck[ i ].suit,
69 ( i + 1 ) % 2 ? 't' : 'n' );
70 }
Cycle through array and print
out data.

Program Output
Eight of Diamonds Ace of Hearts
Eight of Clubs Five of Spades
Seven of Hearts Deuce of Diamonds
Ace of Clubs Ten of Diamonds
Deuce of Spades Six of Diamonds
Seven of Spades Deuce of Clubs
Jack of Clubs Ten of Spades
King of Hearts Jack of Diamonds
Three of Hearts Three of Diamonds
Three of Clubs Nine of Clubs
Ten of Hearts Deuce of Hearts
Ten of Clubs Seven of Diamonds
Six of Clubs Queen of Spades
Six of Hearts Three of Spades
Nine of Diamonds Ace of Diamonds
Jack of Spades Five of Clubs
King of Diamonds Seven of Clubs
Nine of Spades Four of Hearts
Six of Spades Eight of Spades
Queen of Diamonds Five of Diamonds
Ace of Spades Nine of Hearts
King of Clubs Five of Hearts
King of Spades Four of Diamonds
Queen of Hearts Eight of Hearts
Four of Spades Jack of Hearts
Four of Clubs Queen of Clubs

 union
◦ Memory that contains a variety of objects over time
◦ Only contains one data member at a time
◦ Members of a union share space
◦ Conserves storage
◦ Only the last data member defined can be accessed
 union declarations
◦ Same as struct
union Number {
int x;
float y;
};
Union myObject;

 Valid union operations
◦ Assignment to union of same type: =
◦ Taking address: &
◦ Accessing union members: .
◦ Accessing members using pointers: ->

1. Define union
1.1 Initialize variables
2. Set variables
3. Print
1 /* Fig. 10.5: fig10_05.c
2 An example of a union */
3 #include <stdio.h>
4
5 union number {
6 int x;
7 double y;
8 };
9
10 int main()
11 {
12 union number value;
13
14 value.x = 100;
15 printf( "%sn%sn%s%dn%s%fnn",
16 "Put a value in the integer member",
17 "and print both members.",
18 "int: ", value.x,
19 "double:n", value.y );
20
21 value.y = 100.0;
22 printf( "%sn%sn%s%dn%s%fn",
23 "Put a value in the floating member",
24 "and print both members.",
25 "int: ", value.x,
26 "double:n", value.y );
27 return 0;
28 }

Program Output
Put a value in the integer member
and print both members.
int: 100
double:
-92559592117433136000000000000000000000000000000000000000000000.00000
Put a value in the floating member
and print both members.
int: 0
double:
100.000000

Program Output
1 January
2 February
3 March
4 April
5 May
6 June
7 July
8 August
9 September
10 October
11 November
12 December

structure

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