View
234
Download
0
Category
Preview:
DESCRIPTION
3 Recall: #include #define MAXLEN 50 #define MAXN 20 struct StudentRec { char lastname[MAXLEN]; float mark; }; typedef struct StudentRec Student; marks4a.c Record of student last names and marks
Citation preview
1
Introduction to Computer Programming
Lecture 17Structures (Part 2)
Assist. Prof. Dr. Nükhet ÖZBEKEge University
Department of Electrical & Electronics Engineeringnukhet.ozbek@ege.edu.tr
2
Topics• Structure• Arrays of structs• typedef• structs and functions• Pointers to structs• structs within structs• Data structures and modular design
3
Recall:
#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
Record of student last names and marks
4
Student readRecord ( void ){ Student newStudent; printf("Enter last name and mark: "); scanf("%s %f", newStudent.lastname, &(newStudent.mark) ); return newStudent;}
Recall: Functions to read and print a student record
void printRecord ( Student item ){ printf("Last name: %s\n", item.lastname); printf(" Mark: %.1f\n\n", item.mark);}
marks4a.c
5
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
Recall: Sample main: an array of student records
6
Passing a struct Variable
lastname:
mark:
studentA:int main(){ Student studentA; studentA = readRecord(); return 0;}
7
Student readRecord ( void ){ Student newStudent; printf("Enter last name and mark: "); scanf("%s %f", newStudent.lastname, &(newStudent.mark)); return newStudent;}
lastname:mark:
newStudent:
int main(){ Student studentA; studentA = readRecord(); return 0;}
Version 1
Passing a struct Variable (cont)
lastname:
mark:
studentA:
8
Student readRecord ( void ){ Student newStudent; printf("Enter last name and mark: "); scanf("%s %f", newStudent.lastname, &(newStudent.mark)); return newStudent;}
lastname:
mark:
studentA:
lastname:
mark:
newStudent:
Version 1
Passing a struct Variable (cont)
int main(){ Student studentA; studentA = readRecord(); return 0;}
9
Passing a struct Variable (cont)
lastname:
mark:
studentA:int main(){ Student studentA; studentA = readRecord(); return 0;}
10
int main(){ Student studentA; studentA = readRecord(studentA); return 0;}
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
Passing a struct Variable (cont)
11
What if the struct is huge?
Passing a struct Variable (cont)Student readRecord ( Student newStudent ){ printf("Enter last name and mark: "); scanf("%s %f", newStudent.lastname, &(newStudent.mark) ); return newStudent;}
int main(){ Student studentA; studentA = readRecord(StudentA); return 0;}
Version 2
12
Passing a struct Pointer
Pass a pointer to the struct variable
instead!
lastname:
mark:
studentA:
studentPtr:
13
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:
14
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:
15
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:
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
#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)
18
#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)
19
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
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
lastname:
mark:
struct StudentRec{ char lastname[MAXLEN]; float mark;};
typedef struct StudentRec Student;
22
Information required to maintain a class list• Number of students in the class (<= MAXN)• Subject code
class:
lastname:
mark:
lastname:
mark:
lastname:
mark:
Student class[MAXN];
Example: Class Record (cont)
23
Information required to maintain a class list• Number of students in the class (<= MAXN)• Subject code
char subjCode[MAXLEN]; int count; Student class[MAXN];
count:
class:
lastname:
mark:
lastname:
mark:
lastname:
mark:
subjCode:
Example: Class Record (cont)
24
struct ClassRec{ char subjCode[MAXLEN]; int count; Student class[MAXN];};
typedef struct ClassRec ClassList;
Example: Class Record (cont)
count:
class:
lastname:
mark:
lastname:
mark:
lastname:
mark:
subjCode:“Encapsulates” the data needed to maintain a class list
25
ClassList subject[MAXSUBJ];
Example: Department Databasesubject:
26
char deptName[MAXLEN]; int count; ClassList subject[MAXSUBJ];
Example: Department Database (cont)subject:
deptName:
count:
27
Example: Department Database (cont)
subject:
deptName:
count:
struct DatabaseRec{ char deptName[MAXLEN]; int count; ClassList subject[MAXSUBJ];};
typedef struct DatabaseRec Database;
“Encapsulates” the data needed to maintain a database
28
Access to Struct Members
subject:
deptName:
count:
How do I put the mark 97.5
there?Database finalMarks;
Suppose we declare a struct variable:
29
Access to Struct Members (cont)
finalMarks
subject:
deptName:
count:
finalMarks:
30
Access to Struct Members (cont)
finalMarks.subject[1]
subject:
deptName:
count:
finalMarks:
31
Access to Struct Members (cont)
finalMarks.subject[1].class[0]
subject:
deptName:
count:
finalMarks:
32
Access to Struct Members (cont)
finalMarks.subject[1].class[0].mark = 97.5;
subject:
deptName:
count:
finalMarks:
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
Student Record(Student)
Class Record(ClassList)
Department Database
(Database)
readRecord printRecord
readList printListinitList
readDBase printDBaseinitDBase
main
36
Example: Data and Modules
Student Record(Student)
Class Record(ClassList)
Department Database
(Database)
printRecord
Student
readRecordSt
uden
tStudent
main
37
Example: Data and Modules
Student Record(Student)
Class Record(ClassList)
Department Database
(Database)
main
printRecord
Student
printList
Clas sLi st
readList
Cla
ssLi
st
ClassList
initListC
lass
ListC
lassL is treadRecord
Stud
entStudent
38
Example: Data and Modules
Student Record(Student)
Class Record(ClassList)
Department Database
(Database)
main
printDBase
Database
readDBase
Database
Dat
abas
e
initDBaseDatabase
Database
printRecord
Student
printList
Clas sLi st
readList
Cla
ssLi
stClas sLi st
initListClassList
ClassList
readRecordSt
uden
tStudent
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
struct ClassRec{ char subjCode[MAXLEN]; int count;
};
typedef struct ClassRec ClassList;
void initList ( ClassList *list );void readList ( ClassList *list );void printList ( const ClassList *list );
Example: Modules for Class Record
dbase2b.c
Student student[MAXN];
42
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
Example: Modules for Class Record (cont)
43
struct DatabaseRec{ char deptName[MAXLEN]; int count;
};
typedef struct DatabaseRec Database;
void initDBase ( Database *dbase );void readDBase ( Database *dbase );void printDBase ( const Database *dbase );
Example: Modules for Database
dbase2c.c
ClassList subject[MAXSUBJ};
44
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); }}
Example: Modules for Database (cont)
dbase2c.c
45
Example: Modules for Database (cont)
void printDBase ( const Database *dbase ){ int i; printf("\nDEPARTMENT/FACULTY CODE: %s\n", dbase->deptName); for ( i=0; i < dbase->count; i++ ) { }}
dbase2c.c
printList(&(dbase->subject[i]));
void readDBase ( Database *dbase ){ int i; for ( i=0; i < dbase->count; i++ ) {
}}
initList(&(dbase->subject[i]));readList(&(dbase->subject[i]));
46
#include <stdio.h>#include <stdlib.h>
#define MAXLEN 50#define MAXN 100#define MAXSUBJ 5
#include "dbase2a.c"#include "dbase2b.c"#include "dbase2c.c"
int main(){ Database finalMarks;
return 0;}
Example: Test Main Program
dbase2.c
initDBase(&finalMarks);readDBase(&finalMarks);printDBase(&finalMarks);
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
printDBase
Database
readDBase
Database
Dat
abas
einitDBase
Database
Database
printRecord
Student
printList
Clas sList
readList
Cla
ssLi
stCl as sLi st
initListClassList
ClassList
readRecord
Stud
entStudent
48
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
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
/***********************************************************\ * 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. *\***********************************************************/
Example: Data documentation
Recommended