1. Introduction to Computer Programming Lecture 17 Structures (Part 2)
ITCS 102 Computer Programming
Introduction to Computer Programming Lecture 17 Structures (Part 2)
Assist. Prof. Dr. Nükhet ÖZBEK
Ege University
Department of Electrical & Electronics Engineering
Dr. B. KARLIK

2. Topics Structure Arrays of structs typedef structs and functions
Pointers to structs
structs within structs
Data structures and modular design

3. Record of student last names and marks
Recall:
Record of student last names and marks
#include <stdio.h>
#include <stdlib.h>
#define MAXLEN 50
#define MAXN 20
struct StudentRec {
char lastname[MAXLEN];
float mark; };
typedef struct StudentRec Student;
marks4a.c

4. Functions to read and print a student record
Recall:
Functions to read and print a student record
Student readRecord ( void ) {
Student newStudent;
printf("Enter last name and mark: ");
scanf("%s %f", newStudent.lastname, &(newStudent.mark) );
return newStudent; }
void printRecord ( Student item ) {
printf("Last name: %s\n", item.lastname);
printf(" Mark: %.1f\n\n", item.mark); }
marks4a.c

5. Sample main: an array of student records
Recall:
Sample main: an array of student records
int main() {
int count = 0;
Student class[MAXN];
int i;
printf("How many students? ");
scanf("%d", &count);
if (count > MAXN)
printf("Not enough space.\n");
exit(1); }
for (i=0; i < count; i++)
class[i] = readRecord();
printf("\nClass list:\n\n");
printRecord(class[i]);
return 0;
marks4a.c

6. Passing a struct Variable
studentA:
int main() {
Student studentA;
studentA = readRecord();
return 0; }
lastname:
mark:

7. Passing a struct Variable (cont)
Student readRecord ( void ) {
Student newStudent;
printf("Enter last name and mark: ");
scanf("%s %f", newStudent.lastname,
&(newStudent.mark));
return newStudent; }
newStudent:
lastname:
mark:
Version 1
int main() {
Student studentA;
studentA = readRecord();
return 0; }
studentA:
lastname:
mark:

8. Passing a struct Variable (cont)
Student readRecord ( void ) {
Student newStudent;
printf("Enter last name and mark: ");
scanf("%s %f", newStudent.lastname,
&(newStudent.mark));
return newStudent; }
newStudent:
lastname:
mark:
Version 1
int main() {
Student studentA;
studentA = readRecord();
return 0; }
studentA:
lastname:
mark:

9. Passing a struct Variable (cont)
ITCS 102 Computer Programming
Passing a struct Variable (cont)
studentA:
int main() {
Student studentA;
studentA = readRecord();
return 0; }
lastname:
mark:
Dr. B. KARLIK

10. Passing a struct Variable (cont)
Student readRecord ( Student newStudent ) {
printf("Enter last name and mark: ");
scanf("%s %f", newStudent.lastname,
&(newStudent.mark) );
return newStudent; }
Version 2
A similar thing happens here
int main() {
Student studentA;
studentA = readRecord(studentA);
return 0; }

11. Passing a struct Variable (cont)
What if the struct is huge?
Student readRecord ( Student newStudent ) {
printf("Enter last name and mark: ");
scanf("%s %f", newStudent.lastname,
&(newStudent.mark) );
return newStudent; }
Version 2
int main() {
Student studentA;
studentA = readRecord(StudentA);
return 0; }

12. Passing a struct Pointer
Pass a pointer to the struct variable instead!
studentPtr:
studentA:
lastname:
mark:

13. Passing a struct Pointer
studentPtr:
void readRecord ( Student *studentPtr ) {
/* De-reference pointer here. */ }
int main() {
Student studentA;
readRecord( &(studentA) );
return 0; }
mark:
studentA:
lastname:
lastname:

14. Passing a struct Pointer
ITCS 102 Computer Programming
Passing a struct Pointer
studentPtr:
mark:
studentA:
lastname:
To de-reference a pointer to a struct variable:
Style 1: Use the * operator
void readRecord ( Student *studentPtr ) {
printf("Enter last name and mark: ");
scanf("%s %f", (*studentPtr).lastname,
&((*studentPtr).mark) ); }
marks4b.c
Dr. B. KARLIK

15. Passing a struct Pointer
ITCS 102 Computer Programming
Passing a struct Pointer
studentPtr:
mark:
studentA:
lastname:
To de-reference a pointer to a struct variable:
Style 2: Use the -> operator
void readRecord ( Student *studentPtr ) {
printf("Enter last name and mark: ");
scanf("%s %f", studentPtr->lastname,
&(studentPtr->mark)); }
marks4b.c
Dr. B. KARLIK

16. Example: Pointers to Structs-1
#include <stdio.h>
#include <stdlib.h>
#define MAXLEN 50
#define MAXN 20
struct StudentRec {
char lastname[MAXLEN];
float mark; };
typedef struct StudentRec Student;
void readRecord ( Student *studentPtr )
printf("Enter last name and mark: ");
scanf("%s %f", studentPtr->lastname, &(studentPtr->mark)); }
void printRecord ( Student *item )
printf("Last name: %s\n", (*item).lastname);
printf(" Mark: %.1f\n\n", (*item).mark);
marks4c.c

17. Example: Pointers to Structs-1 (cont)
#include <stdio.h>
#include <stdlib.h>
#define MAXLEN 50
#define MAXN 20
struct StudentRec {
char lastname[MAXLEN];
float mark; };
typedef struct StudentRec Student;
void readRecord ( Student *studentPtr )
printf("Enter last name and mark: ");
scanf("%s %f", studentPtr->lastname, &(studentPtr->mark) ); }
void printRecord ( Student *item )
printf("Last name: %s\n", (*item).lastname);
printf(" Mark: %.1f\n\n", (*item).mark);
marks4c.c

18. Example: Pointers to Structs-1 (cont)
#include <stdio.h>
#include <stdlib.h>
#define MAXLEN 50
#define MAXN 20
struct StudentRec {
char lastname[MAXLEN];
float mark; };
typedef struct StudentRec Student;
void readRecord ( Student *studentPtr )
printf("Enter last name and mark: ");
scanf("%s %f", studentPtr->lastname, &(studentPtr->mark) ); }
void printRecord ( Student *item )
printf("Last name: %s\n", (*item).lastname);
printf(" Mark: %.1f\n\n", (*item).mark);
marks4c.c

19. Example: Pointers to Structs-2
int main() {
int count = 0;
Student class[MAXN];
int i;
printf("How many students? ");
scanf("%d", &count);
if (count > MAXN)
printf("Not enough space.\n");
exit(1); }
for (i=0; i < count; i++)
readRecord( &(class[i]) );
printf("\nClass list:\n\n");
printRecord( &(class[i]) );
return 0;
marks4c.c

20. Structs within Structs
A struct can be a member of another struct
Example:
A student record contains the last name, mark (ID Number, first name, etc)
A class list is a collection of student records (number of students, subject code, etc)
A departmental database is a collection of class lists (department name, number of subjects, etc)

21. Example: Student Record
struct StudentRec {
char lastname[MAXLEN];
float mark; };
typedef struct StudentRec Student;
lastname:
mark:

22. Example: Class Record (cont)
Information required to maintain a class list
Number of students in the class (<= MAXN)
Subject code
class:
lastname:
mark:
Student class[MAXN];

23. Example: Class Record (cont)
ITCS 102 Computer Programming
Example: Class Record (cont)
Information required to maintain a class list
Number of students in the class (<= MAXN)
Subject code
count:
class:
lastname:
mark:
subjCode:
char subjCode[MAXLEN];
int count;
Student class[MAXN];
Dr. B. KARLIK

24. Example: Class Record (cont)
“Encapsulates” the data needed to maintain a class list
count:
class:
lastname:
mark:
subjCode:
struct ClassRec {
char subjCode[MAXLEN];
int count;
Student class[MAXN]; };
typedef struct ClassRec ClassList;

25. Example: Department Database
subject:
ClassList subject[MAXSUBJ];

26. Example: Department Database (cont)
ITCS 102 Computer Programming
Example: Department Database (cont)
subject:
deptName:
count:
char deptName[MAXLEN];
int count;
ClassList subject[MAXSUBJ];
Dr. B. KARLIK

27. Example: Department Database (cont)
subject:
deptName:
count:
“Encapsulates” the data needed to maintain a database
struct DatabaseRec {
char deptName[MAXLEN];
int count;
ClassList subject[MAXSUBJ]; };
typedef struct DatabaseRec Database;

28. Access to Struct Members
subject:
deptName:
count:
Suppose we declare a struct variable:
How do I put the mark 97.5 there?
Database finalMarks;

29. Access to Struct Members (cont)
finalMarks:
subject:
deptName:
count:
finalMarks

30. Access to Struct Members (cont)
finalMarks:
subject:
deptName:
count:
finalMarks.subject[1]

31. Access to Struct Members (cont)
finalMarks:
subject:
deptName:
count:
finalMarks.subject[1].class[0]

32. Access to Struct Members (cont)
finalMarks:
subject:
deptName:
count:
finalMarks.subject[1].class[0].mark = 97.5;

33. Data Structures and System Design: Structure Charts
A modular design makes handling of complex data structures easy
A module handles operations on each data structure
The level of the module in the structure chart should (more or less) correspond to the size of the data they handle

34. Structure Charts
A structure chart is a diagram consisting of rectangular boxes, which represent the modules, and connecting arrows
A structure chart is a graphic tool that shows the hierarchy of program modules and interfaces between them
Structure charts include annotations for data flowing between modules

35. Example: Data and Modules
readRecord
printRecord
readList
printList
initList
readDBase
printDBase
initDBase
main
Department Database
(Database)
Class Record
(ClassList)
Student Record
(Student)

36. Example: Data and Modules
main
Department Database
(Database)
Class Record
(ClassList)
Student
Student
Student
Student Record
(Student)
readRecord
printRecord

37. Example: Data and Modules
main
Department Database
(Database)
ClassList
ClassList
ClassList
ClassList
ClassList
Class Record
(ClassList)
initList
readList
printList
Student
Student
Student
Student Record
(Student)
readRecord
printRecord

38. Example: Data and Modules
ITCS 102 Computer Programming
Example: Data and Modules
main
Database
Database
Database
Department Database
(Database)
Database
Database
initDBase
readDBase
printDBase
ClassList
ClassList
ClassList
ClassList
ClassList
Class Record
(ClassList)
initList
readList
printList
Student
Student
Student
Student Record
(Student)
readRecord
printRecord
Dr. B. KARLIK

39. Example: Modules for Student Record
struct StudentRec {
char lastname[MAXLEN];
float mark; };
typedef struct StudentRec Student;
void readRecord ( Student *studentPtr );
void printRecord ( const Student *item );
dbase2a.c

40. Example: Modules for Student Record (cont)
void readRecord ( Student *studentPtr ) {
printf("Enter last name and mark: ");
scanf("%s %f", studentPtr->lastname,
&(studentPtr->mark)); }
void printRecord ( const Student *item ) {
printf("Last name: %s\n", item->lastname);
printf(" Mark: %.1f\n\n", item->mark); }
dbase2a.c

41. Example: Modules for Class Record
struct ClassRec {
char subjCode[MAXLEN];
int count; };
typedef struct ClassRec ClassList;
void initList ( ClassList *list );
void readList ( ClassList *list );
void printList ( const ClassList *list );
Student student[MAXN];
dbase2b.c

42. Example: Modules for Class Record (cont)
void initList ( ClassList *list ) {
printf("\nEnter subject code: ");
scanf("%s", list->subjCode);
printf("How many students? ");
scanf("%d", &(list->count) );
if (list->count > MAXN)
printf("Not enough space.\n");
exit(1); }
dbase2b.c

43. Example: Modules for Database
struct DatabaseRec {
char deptName[MAXLEN];
int count; };
typedef struct DatabaseRec Database;
void initDBase ( Database *dbase );
void readDBase ( Database *dbase );
void printDBase ( const Database *dbase );
ClassList subject[MAXSUBJ};
dbase2c.c

44. Example: Modules for Database (cont)
void initDBase ( Database *dbase ) {
printf("\nEnter department or faculty code: ");
scanf("%s", dbase->deptName);
printf("How many subjects? ");
scanf("%d", &(dbase->count) );
if (dbase->count > MAXSUBJ)
printf("Not enough space.\n");
exit(1); }
dbase2c.c

45. Example: Modules for Database (cont)
ITCS 102 Computer Programming
void readDBase ( Database *dbase ) {
int i;
for ( i=0; i < dbase->count; i++ ) }
initList(&(dbase->subject[i]));
readList(&(dbase->subject[i]));
void printDBase ( const Database *dbase ) {
int i;
printf("\nDEPARTMENT/FACULTY CODE: %s\n",
dbase->deptName);
for ( i=0; i < dbase->count; i++ ) }
printList(&(dbase->subject[i]));
dbase2c.c
Dr. B. KARLIK

46. Example: Test Main Program
ITCS 102 Computer Programming
Example: Test Main Program
#include <stdio.h>
#include <stdlib.h>
#define MAXLEN 50
#define MAXN
#define MAXSUBJ 5
#include "dbase2a.c"
#include "dbase2b.c"
#include "dbase2c.c"
int main() {
Database finalMarks;
return 0; }
initDBase(&finalMarks);
readDBase(&finalMarks);
printDBase(&finalMarks);
dbase2.c
Dr. B. KARLIK

47. Example: Change definition of student record
which modules/files do I need to modify in order to use student ID instead of last name?
main
Database
Database
Database
Database
Database
initDBase
readDBase
printDBase
ClassList
ClassList
ClassList
ClassList
ClassList
initList
readList
printList
Student
Student
Student
readRecord
printRecord

48. Example: Change definition of student record (cont)
ITCS 102 Computer Programming
Example: Change definition of student record (cont)
struct StudentRec {
long IDNumber;
float mark; };
typedef struct StudentRec Student;
void readRecord ( Student *studentPtr );
void printRecord ( const Student *item );
void readRecord ( Student *studentPtr ) {
printf("Enter ID Number and mark: ");
scanf(”%ld %f", &(studentPtr->IDNumber),
&(studentPtr->mark)); }
void printRecord ( const Student *item ) {
printf(”ID Number: %ld\n", item->IDNumber);
printf(" Mark: %.1f\n\n", item->mark); }
dbase1a.c
Dr. B. KARLIK

49. Documentation of Structs
Data documentation, like function documentation, is very important
Can determine a team’s success in completing a large software project
Should include information on:
assumptions and limitations
operations and corresponding modules
correct usage

50. Example: Data documentation
/***********************************************************\
* DATA:
* Database *
* DESCRIPTION:
* A database is a collection of class lists for subjects
* conducted by a school or department.
* USAGE:
* A database variable can store class lists for up to
* MAXSUBJ subjects. The member ‘count’ keeps track of
* the number of class lists in the database.
* A data of this type needs to be initialized using the
* function initDBase() before use. The member `count'
* has to be initialized to a valid value.
* Use the function readDBase() to initialize and read
* data into each class list. Use the function printDBase()
* to print the content of the entire database.
\***********************************************************/