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 nukhet.ozbek@ege.edu.tr Dr. B. KARLIK

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

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

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

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

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

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:

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:

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

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; }

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; }

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

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:

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

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

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

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

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

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

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)

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

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];

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

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;

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

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

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;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Example: Test Main Program ITCS 102 Computer Programming Example: Test Main Program #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; } initDBase(&finalMarks); readDBase(&finalMarks); printDBase(&finalMarks); dbase2.c Dr. B. KARLIK

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

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

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

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. \***********************************************************/