Lecture 13

Izmir Institute of Technology
CE - 104
Lecture 13
References: - C: A software Engineering Approach
1
In this course you will learn
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Structure Data Types
Use “.” operator to access members of a
structure
See how to declare pointers to structure
variables.
Use “ -> ” operator to access members of a
structure when using pointers.
Union Data Types
2
Structures and Unions
Arrays are good for dealing with groups of identical typed variables,
but they are unsatisfactory for managing groups of differently typed
data.
To service groups of mixed data you need to use an aggregate type
called a structure.
Another aggregate type, called a union, enables you to interpret the
same memory locations in different ways.
3
Structures
To keep track of your grades in the CE 104 course we
need to associate student names, their student id
numbers, and their grades corresponding to homeworks
and examinations. And of course, finally their letter
grade.
Without structures we would need to define the
followings:
The name shall consist of 18 characters, the student id
number is a 9 digit number and therefore should be
assigned as a long int, and the grades of homeworks
and exams should be a short int (char would also work).
And finally the grade shall consist of two characters.
char name[19], grade[3];
long int idnum;
short hw, exam;
4
Structures
And if there are 29 students in this class:
char name[29][19], grade[29][3];
long int idnum[29];
short hw[29], exam[29];
Then for each student we would write
strcpy( name[0], "Temel Karadeniz" );
the
following
idnum[0]=30909090;
hw[0]=100;
exam[0]=100;
strcpy( grade[0], "AA" );
Storing the data in this form gets the information into
the computer, but it creates a strange organization.
The information about one person is scattered about
memory instead of being grouped together.
5
Structures
A more natural organization would be to create a single
variable that contains all three pieces of data. C enables
you to do this with a data type called a structure. A
structure is like an array except that each element can
have a different data type. Moreover, the elements in a
structure, called fields or members, have names instead
of subscript values. We like to think of structures as
arrays with personality. To declare a structure to hold CE
104 statistics, you would write
struct ce104stat
typedef struct
{
{
char ce104_name[19], ce104_grade[3];
char ce104_name[19], ce104_grade[3];
long int ce104_idnum;
long int ce104_idnum;
short ce104_hw, ce104_exam;
short ce104_hw, ce104_exam;
} ce104stat ;
};
ce104stat ce104;
ce104stat ce104;
6
Structures
#include <stdio.h>
main()
{
typedef struct
{
char name[19];
long int idnum;
short hw, exam;
char grade[3];
} COURSESTAT;
COURSESTAT ce104[29], *ptr ;
ptr=&ce104[0];
int i=0;
strcpy(ptr->name,"Temel Karadeniz");
ptr->idnum = 1080033211;
ptr->hw = 85;
ce104[i].exam = 98;
strcpy(ce104[i].grade,"AA");
}
printf(" name: %s\n", ce104[i].name);
printf("idnum: %ld\n", ptr->idnum);
printf(" hw: %d\n", ptr->hw);
printf(" exam: %d\n", ce104[i].exam);
printf("grade: %s\n", ce104[i].grade);
7
Structures Data Type
A structure is a user created type definition. It can hold a number
of sub-variables under a single variable.
typedef struct
{
char *isim;
long tc_kimlik;
short dt_yil, dt_ay, dt_gun; } kisisel_bilgi;
8
Structures Data Type
Create a variable that stores the Name, T.C. Identity number, and
the date of birth of each student.
#include <stdio.h>
main()
{
typedef struct
{
char *isim;
long tc_kimlik;
short dt_yil, dt_ay, dt_gun;
} KISISEL_BILGI ;
KISISEL_BILGI
KISISEL_BILGI
KISISEL_BILGI
KISISEL_BILGI
kisi_1;
kisi_2;
kisi_3;
kisi_4;
// To be continued
// Continued ...
kisi_1.isim = "Temel Karadeniz";
kisi_1.tc_kimlik = 1231231231000;
kisi_1.dt_yil = 1995;
kisi_1.dt_ay = 2;
kisi_1.dt_gun = 29;
kisi_2.isim = "Dursun Akdeniz";
kisi_2.tc_kimlik = 1231231231010;
kisi_2.dt_yil = 1994;
kisi_2.dt_ay = 11;
kisi_2.dt_gun = 30;
}
Structures Data Type
Print personal information:
printf("İsim Soyisim : %s\n", kisi_1.isim);
printf("T.C. Kimlik No: %ld\n", kisi_1.tc_kimlik);
printf("Dogum Tarihi : %2d.%2d.%4d\n", kisi_1.dt_gun,
kisi_1.dt_ay,
kisi_1.dt_yil);
printf("\n");
printf("İsim Soyisim : %s\n", kisi_2.isim);
printf("T.C. Kimlik No: %ld\n", kisi_2.tc_kimlik);
printf("Dogum Tarihi : %2d.%2d.%4d\n", kisi_2.dt_gun,
kisi_2.dt_ay,
kisi_2.dt_yil);
Structures Data Type
#include <stdio.h>
main()
{
typedef struct
{
char *isim;
long tc_kimlik;
short dt_yil, dt_ay, dt_gun;
} KISISEL_BILGI ;
KISISEL_BILGI kisiler[10];
kisiler[0].isim = "Temel Karadeniz";
kisiler[0].tc_kimlik = 1231231231000;
kisiler[0].dt_yil = 1995;
kisiler[0].dt_ay = 2;
kisiler[0].dt_gun = 29;
Structures Data Type
kisiler[1].isim = "Dursun Akdeniz";
kisiler[1].tc_kimlik = 1231231231010;
kisiler[1].dt_yil = 1994;
kisiler[1].dt_ay = 11;
kisiler[1].dt_gun = 30;
int i;
for (i=0;i<10;i++)
{
printf(“\n”);
printf("İsim Soyisim : %s\n", kisiler[i].isim);
printf("T.C. Kimlik No: %ld\n", kisiler[i].tc_kimlik);
printf("Dogum Tarihi : %2d.%2d.%4d\n", kisiler[i].dt_gun,
kisiler[i].dt_ay,
kisiler[i].dt_yil);
}
}
Structures Data Type
Example: Vector Arithmetics
#include <stdio.h>
#include <stdlib.h>
typedef struct {
double x;
/* user defined data-type called vector */
/* this is a definition*/
/* no variables are declared */
double y;
/* location is outside any block */
} vector;
vector add(vector vec1, vector vec2) ; /* prototype */
vector sub(vector vec1, vector vec2) ; /* prototype */
double dot(vector vec1, vector vec2) ; /* prototype */
/* continued on next slide */
13
Structures Data Type
/* see explanation of the above in subsequent slides */
void main(void){
vector v1,v2,v3 ={1.0,2.0}; /* three variables of type vector*/
/* v3 initialized to {1.0,2.0} */
v1.x = 2.5;
/* use the . to access individual fields */
v1.y = -1.5;
v2 = v3;
*/
/* can assign all the values with one statement
/* continued on next slide */
Structures Data Type
printf(“v1 = [%f,%f]\n”,
v1.x, v1.y);
printf(“v2 = [%f,%f]\n”,
v2.x, v2.y);
v3 = add(v1,v2);
printf(“add(v1,v2) = [%f,%f]\n”,
v3.x, v3.y);
v3 = sub(v1,v2);
printf(“sub(v1,v2) = [%f,%f]\n”,
printf(“dot(v1,v2) = %f\n”,
return 0;
} /* end of main */
v3.x, v3.y);
dot(v1,v2));
Structures Data Type
vector add(vector vec1, vector vec2){
vector v4 = {vec1.x + vec2.x, vec1.y + vec2.y};
return v4;
} /* end of add */
vector sub(vector vec1, vector vec2){
vector v4 = {vec1.x - vec2.x, vec1.y - vec2.y};
return v4;
} /* end of sub */
double dot(vector vec1, vector vec2){
return (vec1.x * vec2.x) + (vec1.y * vec2.y);
} /* end of dot */
More Examples ?
#include <stdio.h>
#include <stdlib.h>
main()
{
typedef struct {
int appletrees;
/* number of apple trees */
int hazelnuttrees;
/* number of hazelnut trees */
} mygarden;
mygarden.appletrees = 3;
mygarden.hazelnuttrees = 4;
}
Union Data Types
Unions are similar to structures except that the members are overlaid
one on top of another, so members share the same memory.
#include <stdio.h>
main()
{
typedef union
{
short int number_of_students;
short int ogrenci_sayisi;
} DERS_INFO;
DERS_INFO ce104;
ce104.ogrenci_sayisi = 5;
printf("\n No. of students = %d \n", ce104.number_of_students);
}
In this course you have learned
●
●
●
●
●
Structure Data Types
Use “.” operator to access members of a
structure
See how to declare pointers to structure
variables.
Use “ -> ” operator to access members of a
structure when using pointers.
Union Data Types
19