1. Chapter 10 Structures and Unions
PROGRAMMING IN ANSI C

2. 2/23/2019
Question
An array can be used to represent a group of data items of the same type.
Sometimes, we want to represent a collection of data items of different types, but we can't use arrays.

3. 2/23/2019
Question
For example, we want to represent the information of a student, such as: student_number, name, sex, age, entrance_score and address, we can define these like:
struct student {
} ;
int num;
char name[20];
char sex;
int age;
float score;
char addr[30];
These variables are independent, so it is
difficult to reflect
their internal relation.
Structure!

4. 2/23/2019
Defining a Structure
The definition of structure is not for a variable but type.
Like the data type provided by system (such as: int, float, double, char, and so on), the definition of structure used to declare variables.
The difference is: the definition of structure is defined by user.
"Structure" is a constructed data type. It is used to pack data of different types. It is a user-defined type.
A valid identifier, and can be omitted.
struct [tag_name] {
data_type member1;
data_type member2; ……
} ;
struct is a keyword, and can't be omitted.
Can be primary type or derived type.

5. 2/23/2019
Defining a Structure
The definition of structure is the description of the data organization form. It is a description of data type defined by user, not a declaration of variable.
name
num
sex
age
score
addr
2 bytes
20 bytes
1 byte
4 bytes
30 bytes … ……
struct student {
int num;
char name[20];
char sex;
int age;
float score;
char addr[30]; };
Variables in such type organize their elements and require storage in memory according to such form. Each variable requires 59 bytes storage.

6. Declaring Structure Variables
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Declaring Structure Variables
stu1.name
stu1.num
stu1.sex
stu1.age
stu1.score
stu1.addr
2 bytes
20 bytes
1 byte
4 bytes
30 bytes … ……
stu2.name
stu2.num
stu2.sex
stu2.age
stu2.score
stu2.addr
There are 3 ways to declare structure variables:
First define structure type, and then declare structure variables.
struct tag_name {
data_type member1;
data_type member2; ……
} ;
struct tag_name variables list;
struct student
{ int num;
char name[20];
char sex;
int age;
float score;
char addr[30]; };
struct student stu1, stu2;

7. Declaring Structure Variables
2/23/2019
Declaring Structure Variables
Define structure type, at the same time, declare structure variables.
struct tag_name {
data_type member1;
data_type member2; ……
} variables list;
struct student
{ int num;
char name[20];
char sex;
int age;
float score;
char addr[30];
} stu1, stu2;

8. Declaring Structure Variables
2/23/2019
Declaring Structure Variables
Declare structure variables immediately.
struct {
data_type member1;
data_type member2; ……
} variables list;
struct
{ int num;
char name[20];
char sex;
int age;
float score;
char addr[30];
} stu1, stu2;

9. Declaring Structure Variables
2/23/2019
Declaring Structure Variables
Structure members can also be a structure .
struct date
{ int month;
int day;
int year;
} ;
struct student
{ int num;
char name[20];
struct date birthday;
} stu;
struct student
{ int num;
char name[20];
struct date
{ int month;
int day;
int year;
} birthday;
} stu;
num
name
birthday
month
day
year

10. Declaring Structure Variables
2/23/2019
Declaring Structure Variables
A structure member name can be the same as another variable name.
main ( )
{ struct student
{ int num;
char name[20];
} stu;
int num;
num = 0;
stu.num = 1; }

11. Accessing Structure Members
2/23/2019
Accessing Structure Members
Like arrays, we can't read in or output the whole structure variable, and we can't use the whole structure variables to evaluate expression. We must access structure members.
Structure members are not variables, so they should be linked to the structure variables in order to make them meaningful members.
The accessing form: structure variable.member
Member operator (dot operator)
Precedence: 1
Associativity: left to right

12. Accessing Structure Members
2/23/2019
Accessing Structure Members
We can't read in or output the whole structure variable. However, structure variables can be initialized as a whole. A structure variable can be assigned to another.
struct student
{ int num;
char name[20];
char sex;
} stu1, stu2 = {101, "Jack", 'M'};
stu1 = stu2;
scanf ("%d, %s, %c", &stu1.num, stu1.name, &stu1.sex);
printf ("%d, %s, %c", stu1.num, stu1.name, stu1.sex);

13. Accessing Structure Members
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Accessing Structure Members
main()
{ struct date
{ int month;
int day;
int year; };
struct student
{ int num;
char name[20];
struct date birthday;
} stu={101, "Jack", {1, 31, 1986}};
printf ("num: %d\nname: %s\nbirthday: %d-%d-%d\n", stu.num, stu.name, stu.birthday.year, stu.birthday.month, stu.birthday.day) ; }
num: 101
name: Jack
birthday:

14. Accessing Structure Members
2/23/2019
Accessing Structure Members
We can't directly judge whether 2 structure variables are same or not, and we must compare each member.
struct student
{ int num;
char name[20];
} stu1, stu2 = {101, "Jack"};
stu1 = stu2;
if ( stu1 == stu2 )
printf ("OK!");
struct student
{ int num;
char name[20];
} stu1, stu2 = {101, "Jack"};
stu1 = stu2;
if(stu1.num==stu2.num && !strcmp(stu2.name, stu1.name))
printf ("OK!");
Error … : Illegal structure operation in function ...

15. Arrays of Structure num name sex age stu[0] stu[1] 25B
2/23/2019
Arrays of Structure
num
name
sex
age
stu[0]
stu[1]
25B
In an array of structure, each element represents a structure variable.
struct
{ int num;
char name[20];
char sex;
int age;
} stu[2];
struct student
{ int num;
char name[20];
char sex;
int age; };
struct student stu[2];
struct student
{ int num;
char name[20];
char sex;
int age;
} stu[2];

16. Arrays of Structure - Initialization
2/23/2019
Arrays of Structure - Initialization
struct student
{ int num;
char name[20];
char sex;
} stu1[2] = {101, “John”, ‘M’, 102, “Mary", 'F' }, stu2[2] = { {101, "John", 'M'}, {102, "Mary", 'F'} },
stu3[ ] = { {101, "John", 'M'}, {102, "Mary", 'F'} };

17. Arrays of Structure - Accessing Members
2/23/2019
Arrays of Structure - Accessing Members
struct student
{ int num;
char name[20];
char sex;
} stu[2] = {101, "John", 'M' } ;
stu[1].sex = 'F';
strcpy ( stu[1].name, "Mary" );
printf ( "%d", stu1[1].num );

18. Arrays of Structure - Program
2/23/2019
main()
{ int i, j, n=10; char name[20];
struct person
{ char name[20];
int count;
} leader[3] = { "Jack", 0, "Marry", 0, "Tom", 0 };
for ( i=1; i<=n; i++ )
{ scanf ( "%s", name );
for ( j = 0; j < 3; j++ )
if ( strcmp(name, leader[j].name) == 0 )
{ leader[j].count++; break; } }
printf ( "%s: %d\n", leader[j].name, leader[j].count );
Jack 
Marry 
Tom 
Jack : 6
Marry: 3
Tom: 1
Arrays of Structure - Program
count
leader[0]
leader[1]
leader[2]
name
Jack
Marry
Tom
Calculate the ballot of each candidate.