1 Introduction to Computer Programming Lecture 16 Structures (Part 1) Assist. Prof. Dr. Nükhet ÖZBEK Ege University Department of Electrical & Electronics Engineering [email protected]
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1
Introduction to Computer
Programming
Lecture 16
Structures (Part 1)
Assist. Prof. Dr. Nükhet ÖZBEK
Ege University
Department of Electrical & Electronics Engineering
2
Topics
• Structure
• Arrays of structs
• typedef
• structs and functions
• Pointers to structs
• structs within structs
• Data structures and modular design
3
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
4
Structure Definition
Lunchbox
Define a structure called
“Lunchbox” which has the
following compartments:
• a fruit compartment
• a sandwich compartment
• a drink compartment
• A structure is a blueprint
• Example:
5
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
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)
struct LunchBox kids[5] =
{
{1, 370.0, “kofte” },
{2, 100.0, “doner”},
{0, 0.0, “kebap”},
{1, 300.0, “salata”},
{0, 0.0, “”}
};
0 1 2 3 4
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;
0
1
2
kids[index+1].drink =
kids[index - 1].drink;
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);
}
for (i=0; i < 3; i++)
{
printf(“%d, %f, %s\n”,
kids[i].fruit, kids[i].drink,
kids[i].sandwich);
}
0
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
}
for each student in the list
{
output last name and mark
}
14
#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
Example without struct-1
15
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");
for (i=0; i < count; i++)
{
printf("Last name: %s\n", lastname[i]);
printf(" Mark: %.1f\n\n", mark[i]);
}
return 0;
} marks1.c
Example without struct-2
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)
#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
18
#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
Example with struct-1
19
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");
for (i=0; i < count; i++)
{
printf("Last name: %s\n", class[i].lastname);
printf(" Mark: %.1f\n\n", class[i].mark);
}
return 0;
} marks3a.c
Example with struct-2
20
Common Mistake
struct StudentRec
{
char lastname[MAXLEN];
float mark;
};
Do not forget the
semicolon here!
21
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? */
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)
struct StudentRec
{
char lastname[MAXLEN];
float mark;
} studA, studB, class[MAXN];
• We can define a struct, and declare instances
of that struct
24
typedef
• A typedef statement makes an identifier
equivalent to a type specification
struct StudentRec
{
char lastname[MAXLEN];
float mark;
};
struct StudentRec studentA;
struct StudentRec class[MAXN];
Example
without typedef
25
struct StudentRec
{
char lastname[MAXLEN];
float mark;
};
typedef struct StudentRec Student;
Student studA;
Student class[MAXN];
Example
with typedef
typedef (cont)
• The typedef statement makes an
identifier equivalent to a type specification
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 #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
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");
for (i=0; i < count; i++)
{
printf("Last name: %s\n", class[i].lastname);
printf(" Mark: %.1f\n\n", class[i].mark);
}
return 0;
}
marks3b.c
Example with typedef-2
29
Notes on typedef
• Yet another way of using typedef:
typedef struct
{
char lastname[MAXLEN];
float mark;
} Student;
Student studA, studB;
Student class[MAXN];
30
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);
}
31
Function Returning a struct
• A “package” containing several values
main()
{
Student studentA;
studentA = readRecord();
}
Student readRecord ( void )
{
Student newStudent;
printf("Enter last name and mark: ");
scanf("%s %f",newStudent.lastname,&(newStudent.mark));
return newStudent;
} Version 1
32
Function Returning a struct (cont)
Student readRecord ( Student newStudent )
{
printf("Enter last name and mark: ");
scanf("%s %f",newStudent.lastname,&(newStudent.mark));
return newStudent;
}
main()
{
Student studentA;
studentA = readRecord(studentA);
}
Version 2
• A “package” containing several values
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
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");
for (i=0; i < count; i++)
{
printRecord(class[i]);
}
return 0;
} marks4a.c
Example: Structs and Functions-2
35
Passing a struct Pointer
Pass a pointer to
the struct variable
instead!
lastname:
mark:
studentA:
studentPtr:
36
void readRecord ( Student *studentPtr )
{
/* De-reference pointer here. */
}
int main()
{
Student studentA;
readRecord( &(studentA) );
return 0;
}
Passing a struct Pointer
lastname:
mark:
studentA:
studentPtr:
lastname:
37
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
Passing a struct Pointer
studentPtr:
mark:
studentA:
lastname:
38
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
Passing a struct Pointer
studentPtr:
mark:
studentA:
lastname:
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
#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
Example: Pointers to Structs-1 (cont)
41
#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
Example: Pointers to Structs-1 (cont)
42
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");
for (i=0; i < count; i++)
{
printRecord( &(class[i]) );
}
return 0;
} marks4c.c
Example: Pointers to Structs-2
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