Chapter 10 Structures and Unions

1. Chapter 10Structures and Unions PROGRAMMING IN C

2. 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. These variables are independent, so it is difficult to reflect their internal relation. 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: int num; char name[20]; char sex; int age; float score; char addr[30]; struct student { } ; Structure!

4. 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; …… } ; structis a keyword, and can't be omitted. Can be primary type or derived type.

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

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

7. 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 • 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. birthday num name month day year 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;

10. 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 • 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 • 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 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: 1986-1-31

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

16. 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 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. Define a struct stu(num,name,score[3]), assign the values in main(),and output in print()) #include <stdio.h> #include <String.h> struct student{ int num; char name[20]; double score[3]; }; void main() { void print(struct student); struct student stu; stu.num=12345; strcpy(stu.name,"Zhangsan"); stu.score[0]=67.5; stu.score[1]=89; stu.score[2]=78.6; print(stu); } void print(struct student stu) { printf("%d %s %.2f %.2f %.2f",stu.num,stu.name,stu.score[0],stu.score[1],stu.score[2]); printf("\n"); }

19. name count count 0 0 leader[0] Jack 0 0 leader[1] Marry 0 0 leader[2] Tom 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; } } for ( j = 0; j < 3; j++ ) printf ( "%s: %d\n", leader[j].name, leader[j].count ); } Jack  Jack  Marry  Jack  Tom  Marry  Jack  Marry  Jack  Jack  Jack : 6 Marry: 3 Tom: 1 Arrays of Structure - Program • Calculate the ballot of each candidate.