Morteza Noferesti
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Morteza Noferesti
2
The C language provides a facility called typedef for creatingsynonyms for previously defined data type names.
For example, the declaration:
typedef int Length;
Length a, b, len ;
Length numbers[10] ;
makes the name Length a synonym (or alias) for the data type int.
The data type name Length can now be used in declarations in exactlythe same way that the data type int can be used:
typedef char String[50];
typedef int Array[10];
String name;
Array ages;
3
Structures—sometimes referred to as aggregates—are collections ofrelated variables under one name
Structures may contain variables of many different data types—incontrast to arrays that contain only elements of the same data type
Structures are commonly used to define records
Pointers and structures facilitate the formation of more complexdata structures such as linked lists, queues, stacks and trees
Structures are derived data types—they are constructed using objectsof other types
4
struct employee
{char firstName[ 20 ];char lastName[ 20 ];int age;char gender;double hourlySalary;
} Ali, Sara, empDTS[20];
struct employee
{
char firstName[ 20 ];
char lastName[ 20 ];
int age;
char gender;
double hourlySalary;
};
The name "employee" is called a structure tag
5
Members of the same structure type must have uniquenames, but two different structure types may containmembers of the same name without conflict
Each structure definition must end with a semicolon
struct employee
{char Name[ 20 ];char Name[ 20 ]; // Error!!!int age;char gender;double hourlySalary;
} Ali, Sara, empDTS[20];
struct employee Reza, *emp;
struct Student
{char Name[ 20 ]; // OKint age;char gender;
};
struct Student Ce40153[80];
6
A structure cannot contain an instance of itself
For example, a variable of type struct employee cannot bedeclared in the definition for struct employee A pointer to structemployee, however, may be included
A structure containing a member that is a pointer to the samestructure type is referred to as a self-referential structure
struct employee {
// …
double hourlySalary;
struct employee person; /* ERROR */
struct employee *ePtr; /* pointer */
};
7
The structure tag name is optional
If a structure definition does not contain a structure tagname, variables of the structure type may be declaredonly in the structure definition—not in a separatedeclaration
struct
{char firstName[ 20 ];char lastName[ 20 ];int age;char gender;double hourlySalary;
} Ali;
8
Structure definitions do not
reserve any space in memory;
rather, each definition creates a
new data type that is used to
define variables
sizeof(struct …) =
sum of sizeof(members) +
alignment padding
(Processor- and compiler-specific)
struct employee
{
char firstName[ 20 ];
char lastName[ 20 ];
int age;
char gender;
double hourlySalary;
};
struct employee Ali, emp[10];
printf("%d", sizeof(Ali));
printf("%d", sizeof(emp));
printf("%d", sizeof(struct
employee));
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it's much, much easier on the processor if the
compiler arranges it like this:
most compilers will “pad” the structure (as if
with extra, invisible fields) like this:
struct {
char a[3];
short int b;
long int c;
char d[3];
};
10
Individual members of a struct variable may be accessed
using the structure member operator (the dot, "."):
myEmp.firstName ;
employee. firstName; // Error
Or , if a pointer to the struct has been declared and
initialized
employee *emp = &myEmp ;
◦ by using the structure pointer operator :
emp→firstName; // arrow operator
◦ which could also be written as:
(* emp).firstName;
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personageLastNameFirstName
gpaid
20914015314Jafarinezhadomidstudents[0]
20222222290ShekarestaniSamadStudents[1]
2011111111100ShekarestaniKhaje Nezamstudents[2]
students[3]
struct identity sharifC40153[80] = {“Omid", "Jafarinezhad", 14, 9140153, 20,
"Samad", "Shekarestani", 90, 2222222, 20} ;
strcpy(sharifC40153[2].FirstName, "Khaje Nezam");
strcpy(sharifC40153[2].LastName, "Shekarestani");
sharifC40153[2]. age = 100;
sharifC40153[2]. person.id = 11111111;
sharifC40153[2]. person. gpa = 20;
12
bool check_birthday(struct Date today, struct Date myFriend)
{
if ((today.month == myFriend.month) &&
(today.day == myFriend.day))
return (true);
return (false);
}
int main()
{
struct Friend friends[NFRIENDS];
struct Date today = {2017, 11, 25};
// ...
for (i = 0; i < NFRIENDS; i++)
{
if(check_birthday(today, friends[i].Birthday))
printf ("%s %s\n", friends[i].FirstName, oj.LastName) ;
} // …
#define NFRIENDS 10
struct Date
{
unsigned year;
unsigned month;
unsigned day;
};
struct Friend
{
char FirstName[30];
char LastName[30];
struct Date Birthday;
};
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…8 bit …
…8 bit …
…8 bit …
Notice that bit field members of structures are accessedexactly as any other structure member
Padded to be an integral number of words◦ Placement is compiler-specific
struct Flags
{
int f1:3;
unsigned int f2:1;
unsigned int f3:2;
} foo;
foo.f1 = -2;
foo.f2 = 1;
foo.f3 = 2;
1 1 0 1 1 0 … …
f1 f2 f3
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Date create_date1(int month,
int day,
int year)
{
Date d;
d.month = month;
d.day = day;
d.year = year;
return (d);
}
void create_date2(Date *d,
int month,
int day,
int year)
{
d->month = month;
d->day = day;
d->year = year;
}
Date today;
today = create_date1(9, 4, 2008);
create_date2(&today, 9, 4, 2008);
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typedef struct
{
char firstName[ 20 ];
char lastName[ 20 ];
int age;
char gender;
double hourlySalary;
} employee; /* The "alias"
employee Ali; /* Create a struct variable */
16
Structures may not be compared using operators ==
and !=
struct a {
int a; int b;
};
struct a b, c;
b.a = 10;
b.b = 30;
c = b;
if(c == b) // Error
17
Enumeration is a user-defined data type. It is defined using
the keyword enum and the syntax is:
enum tag_name {name_0, …, name_n} ;
The tag_name is not used directly. The names in the braces
are symbolic constants that take on integer values from zero
through n. As an example, the statement:
enum colors { red, yellow, green } ;
◦ creates three constants. red is assigned the value 0, yellow is assigned 1
and green is assigned 2
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#include <stdio.h>
int main( )
{
int March[5][7]={{0,0,1,2,3,4,5},
{6,7,8,9,10,11,12},
{13,14,15,16,17,18,19},
{20,21,22,23,24,25,26},
{27,28,29,30,31,0,0}};
enum days {Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday};
enum week {week_one, week_two, week_three, week_four, week_five};
printf ("Monday the third week of March is March %d\n",
March [week_three] [Monday] );
}
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Values in an enum start with 0, unless specified otherwise, and are
incremented by 1
The identifiers in an enumeration must be unique
Multiple members of an enumeration can have the sameconstant value
Assigning a value to an enumeration constant after it has beendefined is a syntax error
Use only uppercase letters enumeration constant names. This makesthese constants stand out in a program and reminds you thatenumeration constants are not variables
20
enum months {JAN = 1, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT,
NOV, DEC };
enum months month;
/* initialize array of pointers */
const char *monthName[] = { "", "January", "February", "March",
"April", "May", "June", "July", "August", "September", "October",
“November", "December"};
for (month = JAN; month <= DEC; month++ )
{
printf( "%2d%11s\n", month, monthName[month] );
}
21
A union is a derived data type—like a structure—withmembers that share the same storage space
For different situations in a program, some variablesmay not be relevant, but other variables are—so aunion shares the space instead of wasting storage onvariables that are not being used
The members of a union can be of any data type
The number of bytes used to store a union must be atleast enough to hold the largest member
Only one member, and thus one data type, can bereferenced at a time
22
union myDataUnion {
int i;
char c;
float f;
} u1, u2;
union myDataUnion u3;
u1.i = 4;
u1.c = ’a’;
u2.i = 0xDEADBEEF;
c
i
f
23
In a declaration, a union may be initialized with a value
of the same type as the first union member
union a
{
int c; // OK
char b[4];
};
union a test;
test.c = 10;
printf("%d", test.c);
24
A union value doesn’t "know" which case it contains
union AnElt {
int i;
char c;
} elt1, elt2;
elt1.i = 4;
elt2.c = ’a’;
elt2.i = 0xDEADBEEF;
if (elt1 currently has a char) …
How should your program keep track whether
elt1, elt2 hold an int or a char?
Basic answer: Another variable holds that info
25
enum Union_Tag {IS_INT, IS_CHAR};
struct TaggedUnion {
enum Union_Tag tag;
union {
int i;
char c;
} data;
};
Tag every value with its case
26
27
class GradeBook
{
public:void setCourseName( string name )
{
courseName = name; }
string getCourseName()
{
return courseName;
}void displayMessage()
{
cout << "Welcome to the grade book for\n" << getCourseName()
<< "!" << endl;
}
private:string courseName;
};
28
GradeBook book(“MyBook”);
int number;
cin >> number;
cout << “Book ” << book.getCourseName()<< “ has ” << number << “ pages”
<< endl;
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