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# t15 BStructures Functions And Arrays by waheedanjum

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```									            Department of Computer and Information Science,
School of Science, IUPUI

CSCI 230

Structures
Functions and Arrays
Dale Roberts, Lecturer
Computer Science, IUPUI
E-mail: droberts@cs.iupui.edu

Dale Roberts
Using Structures With Functions
Passing structures to functions
Pass entire structure or pass individual members
Both pass call by value
It is not a good idea to pass a structure to or return from function.
The better way is passing a pointer to the structure to the functions
and returning a pointer from function.
To pass structures call-by-reference
Pass reference to it
To pass arrays call-by-value
Create a structure with the array as a member
Pass the structure

Dale Roberts
Using Structures With Functions (cont.)
Example:
day_of_year(struct date *pd)
{
int i, day, leap;

day = pd -> day;
leap = pd->year%4 ==0 && pd->year %100 ==0 || pd->year%400 ==0;
for (i=1; i < pd -> month; i++)
day += day_tab[leap][i];
return (day);
}
The declaration struct date *pd;
says that pd is a pointer to a structure of the type date
If p is a pointer to a structure, then p-> member_of_structure refers to the
particular members, like pd -> year
p-> member_of_structure is equivalent to (*p).member_of_structure
Notice: ‘.’ has higher precedence than ‘*’; *pd.year is wrong, since pd.year
is not a pointer.
Both -> and . associate from left to right. So p -> q -> member
are (p->q)->member.
Example: emp.birthday.month are (emp.birthday).month

Dale Roberts
Using Structures With Functions (cont.)
-> and . both are at the highest precedence (together with () for
function and [] for array subscripts)

Example:
struct {
int *x;
int *y;
} *p;

++p->x;        is equivalent to ++(p->x) /* increment x, not p */
(++p)->x;      /* increment p before access x */
*p->y;         /* fetch whatever y points to */
*p->y++;       /* increments y after accessing whatever y point to */
(*p->y)++;     /* increments whatever y point to, just like *p->y++ */
*p++->y;       /* increments p after accessing whatever y point to */

Dale Roberts
typedef
typedef
Creates synonyms (aliases) for previously defined data types
Use typedef to create shorter type names
Example:
typedef struct card *CardPtr;
Defines a new type name CardPtr as a synonym for type struct card *
typedef does not create a new data type while it only creates an alias
Example:   struct card {
const char *face;
const char *suit;
};
typedef struct card Card;
void fillDeck( Card * const, const char *[], const char *[] );
int main()
{
Card deck[ 52 ];
const char *face[] = {"Ace", "Deuce", "Three", "Four", "Five", "Six",
Seven", "Eight", “Nine", "Ten", "Jack", "Queen", "King"};
const char *suit[] = { "Hearts", "Diamonds", "Clubs", "Spades"};
.. ..
fillDeck( deck, face, suit );
.. ..
}
void fillDeck(Card * const wDeck, const char * wFace[], const char * wSuit[])
{
.. ..
}
Dale Roberts
Array of Structures
Example: (before)                                             struct person_data{
char name[PERSON][NAMESIZE];                                  char name[NAMESIZE];
int tscore[PERSON]                                            int tscore;
int math[PERSON]                          (now)               int math;
int english[PERSON]                                          int english;
} person[PERSON];
Initialization of structure array
struct person_data{
.. .. .. ..                               the inner brace is not necessary
} person[]={
{“Jane”,180,89,91},
{“John”,190,90,100},
    “Jane”,180,89,91,
“John”,190,90,100,
.. .. .. ..                           .. .. .. ..
}; /* similar to 2D array */

Example: using separated arrays                       Example: using pointer to structure

average (int tscore, int math, int                    average (struct person_data
eng, int n)                                                 *person, int n)
{                                                  {
int i, total=0,mathtotal = 0,                    int i, total=0,mathtotal = 0,
engtotal=0;                                      engtotal=0;
for (i=0; i<n, i++) {                                for (i=0; i<n, i++) {
total += *tscore++;                                   total += person->tscore;
mathtotal += *math++;                                 mathtotal += person->math;
engtotal += *eng++;                                   engtotal += person->eng;
}                                                         person++;
}
Dale Roberts
Unions
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 Number value;
Valid union operations
Assignment to union of same type: =
Accessing union members: .
Accessing members using pointers: ->

Dale Roberts
1   /* Fig. 10.5: fig10_05.c
2      An example of a union */
3   #include <stdio.h>
4
5   union number {
Define union
6      int x;
7      double y;
8   };
9
10   int main()
11   {
12      union number value;                             Initialize variables
13
Set variables
14       value.x = 100;
15       printf( "%s\n%s\n%s%d\n%s%f\n\n",              Print
16              "Put a value in the integer member",
17              "and print both members.",
18              "int:   ", value.x,
Program Output
19              "double:\n", value.y );                    Put a value in the integer member
20                                                         and print both members.
int:    100
21       value.y = 100.0;
double:
22       printf( "%s\n%s\n%s%d\n%s%f\n",                   -
23              "Put a value in the floating member",      9255959211743313600000000000000000000000000
24              "and print both members.",                 0000000000000000000.00000
25              "int:   ", value.x,
Put a value in the floating member
26              "double:\n", value.y );
and print both members.
27       return 0;                                         int:    0
28   }                                                     double:
100.000000

Dale Roberts
Bit Fields
Bit field
Member of a structure whose size (in bits) has been specified
Enable better memory utilization
Must be declared as int or unsigned
Cannot access individual bits

Declaring bit fields
Follow unsigned or int member with a colon (:) and an integer constant representing
the width of the field
Example:

struct BitCard {
unsigned face : 4;
unsigned suit : 2;
unsigned color : 1;
};                                             struct Example {
unsigned a : 13;
Unnamed bit field                                           unsigned   : 3;
Field used as padding in the structure                   unsigned b : 4;
}
Nothing may be stored in the bits
Unnamed bit field with zero width aligns next bit field to a new storage unit boundary

Dale Roberts
Enumeration Constants
Enumeration
Set of integer constants represented by identifiers
Enumeration constants are like symbolic constants whose values are
automatically set
Values start at 0 and are incremented by 1
Values can be set explicitly with =
Need unique constant names
Example:
enum Months { JAN = 1, FEB, MAR, APR, MAY, JUN, JUL,
AUG, SEP, OCT, NOV, DEC};
Creates a new type enum Months in which the identifiers are set to the
integers 1 to 12
Enumeration variables can only assume their enumeration constant
values (not the integer representations)

Dale Roberts
1    /* Fig. 10.18: fig10_18.c
2        Using an enumeration type */
3    #include <stdio.h>
4
5    enum months { JAN = 1, FEB, MAR, APR, MAY, JUN,
6                    JUL, AUG, SEP, OCT, NOV, DEC };
7
8    int main()
9    {
10       enum months month;
11       const char *monthName[] = { "", "January", "February",
12                                      "March", "April", "May",     1     January
13                                      "June", "July", "August",    2    February
3       March
14                                      "September", "October",      4       April
15                                      "November", "December" };    5         May
16                                                                   6        June
7        July
17       for ( month = JAN; month <= DEC; month++ )                  8      August
18          printf( "%2d%11s\n", month, monthName[ month ] );        9   September
19                                                                  10     October
11    November
20       return 0;                                                  12    December
21 }

Dale Roberts
Storage Management
C supports 4 functions, malloc(), calloc(),free(),
and cfree() for storage management
malloc(n):
allocate a node while its content is still ‘garbage’
n is an integer, indicating the size of memory in byte which you would like
to allocate
malloc() return a character pointer to that memory
So, you have to use cast operator (type), to change the type of the
pointer.
Example:
int *ip;
ip = (int*) malloc(sizeof(int));
struct treeNode *tp;
tp = (struct tnode *) malloc(sizeof(struct tnode));

Dale Roberts
Storage Management (cont.)
free(p):
free() will release the memory allocated by malloc().
p is the pointer containing the address returning from malloc().
Example:
int *ip;
ip = (int*) malloc(sizeof(int));
... .. ..
free(ip);      /* Question: can you free(ip) after ip++ ? */

Example:
struct treeNode *tp;
tp=(struct treeNode *)malloc(sizeof(struct treeNode ));
... .. ..
free(tp);
When there is no further memory, malloc() will return NULL pointer. It is a
good idea to check the returning value of malloc().
if ((ip=(int *)malloc(sizeof(int))) == NULL){
printf(“\nMemory is FULL\n”);
exit(1);
}
When you free the memory, you must be sure that you pass the original
address returning from malloc() to function free(). Otherwise, system
exception may be happened
Dale Roberts
Storage Management (cont.)
calloc(n,size):
calloc() allow you to allocate an n elements array of same data type.
Because n can be an integer variable, you can use calloc() to allocate a
dynamic size array.
n is the element number of array that you want to allocate.
size is the number of byte of each element.
Unlike malloc(), calloc() guarantees that memory contents are all zero
Example: allocate an array of 10 elements
int *ip;
ip = (int*) calloc(10, sizeof(int));

*(ip+1) refer to the 2nd element, the same as ip[1]
*(ip+i) refer to the i+1th element, the same as ip[i]
Like malloc(), calloc() will return NULL, if no further memory is available.
cfree(p):
cfree() releases the memory allocated by calloc().
Example:
cfree(ip);
Dale Roberts

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