1. Introduction to Computer Programming Lecture 16 Structures (Part 1)
ITCS 102 Computer Programming
Introduction to Computer Programming Lecture 16 Structures (Part 1)
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. ITCS 102 Computer Programming
What is a Structure?
In C, we can define our own data types that represent structured collections of data
A collection of related variables under one aggregate name
May contain variables of different types
Using structures:
Define the structure
Declare/Initialize instances of the structure
Access members of an instance of the structure
Dr. B. KARLIK

4. ITCS 102 Computer Programming
Structure Definition
A structure is a blueprint
Example:
Lunchbox
Define a structure called “Lunchbox” which has the following compartments:
a fruit compartment
a sandwich compartment
a drink compartment
Dr. B. KARLIK

5. Structure Definition (cont)
ITCS 102 Computer Programming
Structure Definition (cont)
A struct is used to specify the blueprint
The members specify different aspects of a struct
Example:
struct LunchBox {
int fruit;
float drink;
char sandwich[MAXN]; };
Lunchbox
Dr. B. KARLIK

6. Structure Variable
Instance of a structure: actual series of contiguous memory locations for storage
struct LunchBox ali;
struct LunchBox veli,ayse,fatma;
struct LunchBox kids[5];

7. Initializing a struct Variable
struct LunchBox ali = {1,370.0,“kofte”};

8. Initializing a struct Variable (cont)1 2 3 4
struct LunchBox kids[5] = {
{1, 370.0, “kofte” },
{2, 100.0, “doner”},
{0, 0.0, “kebap”},
{1, 300.0, “salata”},
{0, 0.0, “”} };

9. Members of a struct Variable
struct LunchBox ali, veli;
veli.drink = 0.0;
veli.fruit = 0;
strcpy(veli.sandwich,“doner”);
ali.fruit = 1;
strcpy(ali.sandwich, “kofte”);
ali.drink = 300.0;

10. Members of a struct Variable
struct LunchBox kids[3];
int index = 1;
kids[0].drink = 300.0;
kids[0].fruit = 1;
strcpy(kids[2].sandwich,“kofte”);
kids[index].fruit = 3; 1
kids[index+1].drink =
kids[index - 1].drink; 2

11. Input/Output of struct
Library functions printf() and scanf() do not have format conversion specifiers for structs
Input/Output for each member only
struct LunchBox ayse;
scanf(“%d”, &(ayse.fruit));
scanf(“%f”, &(ayse.drink));
scanf(“%s”, ayse.sandwich);
printf(“%d, %f\n”,
ayse.fruit, ayse.drink);
printf(“%s\n”, ayse.sandwich);

12. Input/Output of struct (cont)
struct LunchBox kids[3];
int i = 0;
for (i=0; i < 3; i++) {
scanf(“%d %f %s”,
&(kids[i].fruit),&(kids[i].drink),
kids[i].sandwich); }
printf(“%d, %f, %s\n”,
kids[i].fruit, kids[i].drink, 1 2

13. Example: Student Record
Write a program to read in and print a list of student last names and test marks
input number of students
for each student in the list {
input last name and mark }
output last name and mark

14. Example without struct-1
ITCS 102 Computer Programming
Example without struct-1
#include <stdio.h>
#include <stdlib.h>
#define MAXLEN 50
#define MAXN 20
int main() {
char lastname[MAXN][MAXLEN];
float mark[MAXN];
int count = 0;
int i;
printf("How many students? ");
scanf("%d", &count);
marks1.c
Dr. B. KARLIK

15. Example without struct-2
if (count > MAXN) {
printf("Not enough space.\n");
exit(1); }
for (i=0; i < count; i++)
printf("Enter last name and mark: ");
scanf("%s %f", lastname[i], &mark[i]);
printf("\nClass list:\n\n");
printf("Last name: %s\n", lastname[i]);
printf(" Mark: %.1f\n\n", mark[i]);
return 0;
marks1.c

16. Example: Student Record
Define a struct: StudentRec
struct StudentRec {
char lastname[MAXLEN];
float mark; };
Easy to extend later to include ID number, first name, etc

17. Example with struct (testing)
ITCS 102 Computer Programming
Example with struct (testing)
#include <stdio.h>
#define MAXLEN 50
struct StudentRec {
char lastname[MAXLEN];
float mark; };
int main()
struct StudentRec studA;
struct StudentRec studB;
printf("Enter last name and mark for student A: ");
scanf("%s %f", studA.lastname, &(studA.mark));
printf("Enter last name and mark for student B: ");
scanf("%s %f", studB.lastname, &(studB.mark));
printf("Student A: %s\t%f\n", studA.lastname, studA.mark);
printf("Student B: %s\t%f\n", studB.lastname, studB.mark);
return 0; }
marks2a.c
Dr. B. KARLIK

18. ITCS 102 Computer Programming
Example with struct-1
#include <stdio.h>
#include <stdlib.h>
#define MAXLEN 50
#define MAXN 20
struct StudentRec {
char lastname[MAXLEN];
float mark; };
int main()
struct StudentRec class[MAXN];
int count = 0;
int i;
printf("How many students? ");
scanf("%d", &count);
marks3a.c
Dr. B. KARLIK

19. Example with struct-2 { printf("Not enough space.\n"); exit(1); }
if (count > MAXN) {
printf("Not enough space.\n");
exit(1); }
for (i=0; i < count; i++)
printf("Enter last name and mark: ");
scanf("%s %f", class[i].lastname, &(class[i].mark));
printf("\nClass list:\n\n");
printf("Last name: %s\n", class[i].lastname);
printf(" Mark: %.1f\n\n", class[i].mark);
return 0;
marks3a.c

20. Do not forget the semicolon here!
Common Mistake
struct StudentRec {
char lastname[MAXLEN];
float mark; };
Do not forget the semicolon here!

21. ITCS 102 Computer Programming
Notes on structs
Initialization vs. Assignment
struct StudentRec studA = {“Ali”, 90};
struct StudentRec studA;
studA = {“Ali”, 90};
struct StudentRec studA = {“Ali”, 90};
struct StudentRec studB;
studB = studA; /* struct contains pointers? */
Dr. B. KARLIK

22. Notes on structs (cont)
struct variables cannot be compared
We can perform member comparisons only
if (studA == studB) {
printf(“Duplicate data.\n”); }
if (strcmp(studA.lastname, studB.lastname) == 0
&& (studA.mark == studB.mark) ) {
printf(“Duplicate data.\n”); }

23. Notes on structs (cont)
We can define a struct, and declare instances of that struct
struct StudentRec {
char lastname[MAXLEN];
float mark;
} studA, studB, class[MAXN];

24. ITCS 102 Computer Programming
typedef
A typedef statement makes an identifier equivalent to a type specification
struct StudentRec {
char lastname[MAXLEN];
float mark; };
Example without typedef
struct StudentRec studentA;
struct StudentRec class[MAXN];
Dr. B. KARLIK

25. typedef (cont)
The typedef statement makes an identifier equivalent to a type specification
struct StudentRec {
char lastname[MAXLEN];
float mark; };
typedef struct StudentRec Student;
Example with typedef
Student studA;
Student class[MAXN];

26. Example with typedef (testing)
#include <stdio.h>
#define MAXLEN 50
struct StudentRec {
char lastname[MAXLEN];
float mark; };
typedef struct StudentRec Student;
int main()
Student studA;
Student studB;
printf("Enter last name and mark for student A: ");
scanf("%s %f", studA.lastname, &(studA.mark));
printf("Enter last name and mark for student B: ");
scanf("%s %f", studB.lastname, &(studB.mark));
printf("Student A: %s\t%f\n", studA.lastname, studA.mark);
printf("Student B: %s\t%f\n", studB.lastname, studB.mark);
return 0; }
marks2b.c

27. Example with typedef-1 marks3b.c #include <stdio.h>
#include <stdlib.h>
#define MAXLEN 50
#define MAXN 20
struct StudentRec {
char lastname[MAXLEN];
float mark; };
typedef struct StudentRec Student;
int main()
int count = 0;
Student class[MAXN];
int i;
printf("How many students? ");
scanf("%d", &count);
marks3b.c

28. Example with typedef-2 marks3b.c { printf("Not enough space.\n");
if (count > MAXN) {
printf("Not enough space.\n");
exit(1); }
for (i=0; i < count; i++)
printf("Enter last name and mark: ");
scanf("%s %f", class[i].lastname, &(class[i].mark) );
printf("\nClass list:\n\n");
printf("Last name: %s\n", class[i].lastname);
printf(" Mark: %.1f\n\n", class[i].mark);
return 0;
marks3b.c

29. ITCS 102 Computer Programming
Notes on typedef
Yet another way of using typedef:
typedef struct {
char lastname[MAXLEN];
float mark;
} Student;
Student studA, studB;
Student class[MAXN];
Dr. B. KARLIK

30. Passing a struct to a Function
ITCS 102 Computer Programming
Passing a struct to a Function
As always, the formal parameters are copies of the actual parameters
void printRecord ( Student item ) {
printf("Last name: %s\n", item.lastname);
printf(" Mark: %.1f\n\n", item.mark); }
main() {
Student studentA = {“Gauss”, 99.0};
printRecord(studentA); }
Dr. B. KARLIK

31. Function Returning a struct
A “package” containing several values
Student readRecord ( void ) {
Student newStudent;
printf("Enter last name and mark: ");
scanf("%s %f",newStudent.lastname,&(newStudent.mark));
return newStudent; }
Version 1
main() {
Student studentA;
studentA = readRecord(); }

32. Function Returning a struct (cont)
A “package” containing several values
Student readRecord ( Student newStudent ) {
printf("Enter last name and mark: ");
scanf("%s %f",newStudent.lastname,&(newStudent.mark));
return newStudent; }
Version 2
main() {
Student studentA;
studentA = readRecord(studentA); }

33. Example: Structs and Functions-1
#include <stdio.h>
#include <stdlib.h>
#define MAXLEN 50
#define MAXN 20
struct StudentRec {
char lastname[MAXLEN];
float mark; };
typedef struct StudentRec Student;
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

34. Example: Structs and Functions-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++)
class[i] = readRecord();
printf("\nClass list:\n\n");
printRecord(class[i]);
return 0;
marks4a.c

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

36. 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:

37. 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

38. 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

39. 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

40. 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

41. 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

42. 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