Chapter9 Structure

7/29/2019 Chapter9 Structure

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User Defined Data Types - updated NI@2006 1

Chapter 10: User Defined Data Types

Objectives: In this chapter you will learn about,Introduction

Declaring Structure Type & StructureVariables

Referring and initializing structure elements

Passing structures to a function

Using typedef

Example using structureEnumeration constants


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Introduction

So far we have only used data types which have

been defined by C such as int, double and char.It is also possible to create our own data types.

A user defined data type is called a structure.

A structure can contain both built-in data typesand another structure.

The concept of structure is pretty much thesame as arrays except that in an array, all the

data is of the same types but in a structure, thedata can be of different types.


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Definition

A structure is a derived data type that

represents a collection of a related dataitems called components (or members)that are not necessarily of the same data

type.


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General syntax:

struct structure_name {data_type element1;

data_type element2;

. . .

};Example:

struct student {

char name[20];

int studentID;char major[50];

};

Declaring Structure TypeAlso called as structure tag

Components / members


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Declaring Structure VariablesAfter declaring a structure type, we may

declare variables that are of that type. Astructure variable declaration requires:

The keyword struct

The structure type name

A list of members (variable names) separated bycommas

A concluding semicolon

Then, assume that variable of structure typestudent is my_student. So the declarationshould be written as;

struct student my_student;


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Based on example: struct student

By including this declaration in our program,

we are informing the compiler about a newdata type which is a user defined data type.

The declaration just makes the compileraware the existent of new data type but does

not take an action yet.

Based on the declaration of


causes the compiler to reserve memoryspace for variable my_student and thecomponents of its structure.


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Structure variable Components Values

name

major

studentID

Simon

0078

CS

my_student

Conceptual memory structure variable my_student of type

student(assuming that the components of variable

my_student have already been assigned values)



It is possible to combine the

declarations of a structure type and astructure variable by including the nameof the variable at the end of the

structure type declaration.struct student {

char name[20];

int studentID;

char major[50];};


struct student {

char name[20];

int studentID;

char major[50];} my_student;

=



Declaring Nested StructureMembers of a structure declaration can

be of any type, including anotherstructure variable.

Suppose we have the followingstructure declaration, which is a

member of struct type student:struct address {

int no;

char street[20];

int zipcode;

};



We can rewrite the structure student

declaration as follow:

This structure type student can be

written as;

struct student {

char name[20];

int studentID;

char major[50];struct address addr;

} ;



struct student {

char name[20];

int studentID;

char major[50];

struct address{

int no;

char street[20];int zipcode;

};

} ;



Referring and Initializing Structure Elements

A structure contains many elements. Each elements of astructure can be referred to / accessed by using thecomponent selection operator. (dot).

Let us use the structure student which we have seen before asan example:

Therefore to refer to the element of a structure, we may writeas follow;

my_student.name;my_student.studentID;my_student.major;

struct student {

char name[20];

int studentID;

char major[50];

};




Therefore, we can initialize each elements of

a structure individually such as:struct student my_student;my_student.studentID = 10179;

Or we can initialize the structure while we are

creating an instance of the structure:struct student my_student = {Ahmad, 10179, IT}

Notice that it is possible to use the =operator on a struct variable. When the =sign is used, each elements of the structureat the right hand side is copied into thestructure at the left hand side.



Examplestruct birthdate {

int month;

int day;

int year;

};

struct birthdate Picasso = {10, 25, 1881};printf(Picasso was born : %d/%d/%d\n, Picasso.day,

Picasso.month, Picasso.year);

Output :Picasso was born : 25/10/1881



Passing Structures to a Function

Call by Value:

We can pass the student structure that we havecreated before to a function called display( ) asfollows:

void display (struct student); /* function prototype */

display (student1); /* function call */

void display (struct student s1); /* function header */where student1 is a variable of type struct student.

In the above function, a copy of the student structure

will be created locally for the use of the function.Anychanges to the structure inside the function will notaffect the actual structure.



Example Using Structure: Call by value

#include #include

struct student{char name[20];int id;

};

void display(struct student); /* function prototype */

void main(void)

{struct student student1;

strcpy(student1.name, "Ahmad"); /*initialising variable */student1.id = 12345; /*initialising variable */

display(student1);}

void display(struct student s1) /* make a local copy of the structure */{

printf("Name: %s\n", s1.name);printf("ID: %d\n", s1.id);

}



Example Using Structure: A Function that return a structure

#include #include

struct student{

char name[20];int id;

};

struct student read(void); /* function prototype */

void main(void){

struct student student1;

student1 = read(); /*function call */printf("Name: %s", student1.name);printf("\nID: %d\n", student1.id);

}

struct student read(void){

struct student s1;

printf("Enter name:");scanf("%s",s1.name); /* alternative: gets(s1.name); */printf("Enter ID:");scanf("%d",&s1.id);

return s1;}


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Call by reference

It is also possible to use pointers and pass the referenceof the structure to the function. This way, any changesinside the function will change the actual structure aswell.

To pass a structure variable as a reference, the Read( )function can be written this way:

void Read(struct student *); /* function prototype */Read(&student1); /* function call */void Read(struct student *s1); /* function header */

where student1 is a variable of type struct student.


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Take note that when a structure is declared as a

pointer, the elements in the structure cannot bereferred to using the . operator anymore. Instead,they need to be accessed using the -> operator(indirect component selection operator).

For example:void Read(struct student *s1)

{s1->studentID = 10179;scanf(%s, s1->name);

}


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Example Using Structure: Call by reference

#include #include

struct student{


};

void Read (struct student *); /* function prototype*/

void main(void){

struct student student1;

Read(&student1); /* function call: passing reference */

printf("Name: %s", student1.name);printf("\nID: %d\n", student1.id);

}

void Read (struct student *s1) /* function header, receive structure as a pointer variable */{

printf("Enter name:");scanf("%s",s1->name); /* you can also use: gets(s1->name) */printf("Enter ID:");scanf("%d",&s1->id);

}


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Using typedefin Structure Declarations

The keyword typedefprovides a

mechanism for creating synonyms(aliases) for previously defined datatypes.

Here is an example on how to usetypedef when declaring a structure:

struct student {

char name[20];

int studentID;

char major[50];

struct address addr;

} ;


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By using typedef:

typedef struct student StudentData;

we are now aliasing the structure with aname to be used throughout the program. Soinstead of writing the word struct beforedeclaring a struct variable like the following


we can now write:

StudentData my_student;

We could use the alias name when passingthe structure to a function:

void display(StudentData s1);


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#include #include

struct student{


};

typedef struct student StudentData;

void display(StudentData); /* function prototype */

void main(void)

{StudentData student1;

strcpy(student1.name, "Ahmad");student1.id = 12345;

display(student1);}

void display(StudentData s1){

printf("Name: %s\n", s1.name);printf("ID: %d\n", s1.id);

}

Example : using typedef

l f


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Example: Array of structure

#include #define NUM_STUDENTS 10

struct student {int studentID;char name[20];int score;char grade;

};typedef struct student StudentData;void Read (StudentData student[]);void CountGrade (StudentData student[]);

void main ( ){

StudentData student[NUM_STUDENTS];Read(student);CountGrade(student);

}


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void Read (StudentData student[]){

int i;for (i = 0; i < NUM_STUDENTS; i++) {

printf("Enter the studentID: ");scanf("%d", &student[i].studentID);printf("Enter the name: ");

scanf("%s", student[i].name);printf("Enter the score: ");scanf("%d", &student[i].score);printf("\n");

}}


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void CountGrade (StudentData student[])

{

int i;

for (i = 0; i < NUM_STUDENTS; i++) {

if (student[i].score > 90)

student[i].grade = 'A';

else if (student[i].score > 80)

student[i].grade = 'B';

else if (student[i].score > 65)student[i].grade = 'C';

else if (student[i].score > 50)

student[i].grade = 'D';

else

student[i].grade = 'F';printf("The grade for %s is %c\n", student[i].name, student[i].grade);

printf("\n");

}

}


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/* Sample Output

Enter the studentID: 789654

Enter the name: Salman

Enter the score: 96

Enter the studentID: 741258

Enter the name: Jack

Enter the score: 79

::

:

The grade for Salman is A

The grade for Jack is C:

:

Press any key to continue

*/

E ample


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Example#include

struct car{

char maker[20];char model[20];

int year;

};

void input(struct car*);void output(char*, char*, int*);

void main()

{

struct car firstcar;

input (&firstcar);output(firstcar.maker, firstcar.model, &firstcar.year);

printf("End of my act!\n");}


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void input(struct car *sp)

{

printf("What is the maker of your car? ");gets(sp->maker);

printf("What is the model of your car? ");

gets(sp->model);

printf("What year is your car? ");

scanf("%d", &sp->year);

}

void output(char *sp1, char*sp2, int*sp3)

{

printf("Your car is : %s, %s, %d\n", sp1, sp2, *sp3);

printf("Nice car\n");}


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/* Sample output

What is the maker of your car? HondaWhat is the model of your car? Stream

What year is your car? 2003

Your car is : Honda, Stream, 2003

Nice carEnd of my act!

Press any key to continue

*/

E ti C t t


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Enumeration Constants

An enumeration, introduced by the keywordenum, is a set of integer constants representedby identifiers. (to specify one after another)

Example:

enum islamic_months {

muharam, safar, rabiulawal, rabiulakhir,

jamadilawal, jamadilakhir, rejab, syaaban,

ramadhan, syawal, zulkaedah, zulhijjah

};

Each of the identifiers actually has a value,starting with 0 (unless specified otherwise).Therefore, we can treat them as integers.


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If we want the enumeration to start with avalue other than 0, we can assign the valueto the first identifier:

enum islamic_months {

muharam = 1, safar, rabiulawal, rabiulakhir,

jamadilawal, jamadilakhir, rejab, syaaban,ramadhan, syawal, zulkaedah, zulhijjah

};

Same as with the other data types, before an

enum can be used, a variable needs to bedeclared:

enum islamic_months months;


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There are cases where it is appropriate for usto use an enum. This is an example of such acase:

enum islamic_months months;

GetMonth (&months);

switch (months) {

case muharam:

. . .

break;

case safar:

. . .

break;

. . .

}


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This is another case where it is appropriate touse an enum:

enum Boolean {FALSE, TRUE};

void main ( ) {

int list[];

Boolean found;

Read(list);

found = Search(list);

if (found == TRUE)

printf(FOUND!!);

else

printf(Cannot find the requested item);

}


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#include

enum months {JAN = 1, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP,OCT, NOV, DEC};

void main ( ) {enum months month;

char *monthsName[] = {January, February, March,April, May, June, July, August, September,October, November, December};

for (month = JAN; month


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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

SUMMARY


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SUMMARYIn this chapter you have learnt about

Structure type and variable declarationsHow structure members can be accessed

How structure can be initialized

Passing structure to functionEnumeration

T.H.E E.N.D

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Chapter9 Structure

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