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 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

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

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

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

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];

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

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, “”} };

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;

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

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);

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

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

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

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

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

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

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

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

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

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

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”); }

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];

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

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];

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

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

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

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

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

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(); }

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); }

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

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

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