itei222 - better structure supplementals

8/13/2019 ITEI222 - Better Structure Supplementals

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Structures

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)


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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;

=


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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;

};


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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;

} ;


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struct student {

char name[20];

int studentID;

char major[50];

struct address{

int no;

char street[20];int zipcode;

};

} ;


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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];

};



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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 = {Jared, 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.


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Examplestruct birthdate {

int month;

int day;

int year;

};

struct birthdate Picasso = {10, 25, 1881};cout


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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.


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Example Using Structure: Call by value

struct student{char name[20];

int id;};

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

void main(){

struct student student1;

strcpy(student1.name, Jared"); /*initializing variable */student1.id = 12345; /*initializing variable */

display(student1);}

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

cout


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Example Using Structure: A Function that return a structure

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

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

void main( ){


student1 = read(); /*function call */

cout s1.id;

return s1;}


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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;cin >> s1->name;

}


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Example Using Structure: Call by reference


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

void main(void){


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

cout > s1->name;cout \nEnter ID:;cin >> 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

struct studentmy_student;

we can now write:

StudentDatamy_student;

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

void display(StudentData s1);


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};

typedef struct student StudentData;

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

void main(){

StudentDatastudent1;

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

display(student1);}

void display(StudentDatas1){

cout


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Example: Array of structure#define NUM_STUDENTS 10struct 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++) {

cout > student[i].name;cout


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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';cout


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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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Examplestruct 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

*/

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