C++ Programming: From Problem Analysis to Program Design, Fifth Edition. Chapter 11: Records (structs)

Transcription

1 C++ Programming: From Problem Analysis to Program Design, Fifth Edition Chapter 11: Records (structs)

2 Objectives In this chapter, you will: Learn about records (structs) Examine various operations on a struct Explore ways to manipulate data using a struct Learn about the relationship between a struct and functions Discover how arrays are used in a struct Learn how to create an array of struct items 2

3 Records (structs) struct: collection of a fixed number of components (members), accessed by name Members may be of different types Syntax: 3

4 Records (structs) (cont'd.) A struct is a definition, not a declaration 4

5 Records (structs) (cont'd.) 5

6 Accessing struct Members The syntax for accessing a struct member is: The dot (.) is an operator, called the member access operator 6

7 Accessing struct Members (cont'd.) To initialize the members of newstudent: newstudent.gpa = 0.0; newstudent.firstname = "John"; newstudent.lastname = "Brown"; 7

8 Accessing struct Members (cont'd.) More examples: cin >> newstudent.firstname; cin >> newstudent.testscore >> newstudent.programmingscore; score = (newstudent.testscore + newstudent.programmingscore) / 2; 8

9 Accessing struct Members (cont'd.) if (score >= 90) newstudent.coursegrade = 'A'; else if (score >= 80) newstudent.coursegrade = 'B'; else if (score >= 70) newstudent.coursegrade = 'C'; else if (score >= 60) newstudent.coursegrade = 'D'; else newstudent.coursegrade = 'F'; 9

10 Assignment Value of one struct variable can be assigned to another struct variable of the same type using an assignment statement The statement: student = newstudent; copies the contents of newstudent into student 10

11 Assignment (cont'd.) The assignment statement: student = newstudent; is equivalent to the following statements: student.firstname = newstudent.firstname; student.lastname = newstudent.lastname; student.coursegrade = newstudent.coursegrade; student.testscore = newstudent.testscore; student.programmingscore=newstudent.programmingscore; student.gpa = newstudent.gpa; 11

12 Comparison (Relational Operators) Compare struct variables member-wise No aggregate relational operations allowed To compare the values of student and newstudent: 12

13 struct Input / Output No aggregate input/output operations on a struct variable Data in a struct variable must be read one member at a time The contents of a struct variable must be written one member at a time 13

14 struct Variables and Functions A struct variable can be passed as a parameter by value or by reference A function can return a value of type struct 14

15 Arrays versus structs 15

16 Arrays in structs Two key items are associated with a list: Values (elements) Length of the list Define a struct containing both items: 16

17 Arrays in structs (cont'd.) 17

18 Arrays in structs (cont'd.) 18

19 structs in Arrays 19

20 structs in Arrays (cont d.) 20

21 structs in Arrays (cont d.) 21

22 structs within a struct versus 22

23 #include <iostream> #include <fstream> #include <string> using namespace std; struct namee { }; string first; string middle; string last; struct birth_date { }; int day; int mon; int year; Struct in File (example)..1 struct employeeinfo { namee na; birth_date bd; float salary; float tax; int phon_num[3]; }; int main() { employeeinfo emp1; ifstream in;...2 ofstream outf;...2 outf.open("waf.txt",ios::app);..3 23

24 emp1.na.first="wafa"; emp1.na.middle="ali"; Struct in File (example). emp1.na.last="al-tarawneh"; cout<<" enter an employee birth date : "; cin>>emp1.bd.day; cin>>emp1.bd.mon>>emp1.bd.year; cout<<"\n enter a salary : ;cin>>emp1.salary; emp1.tax=emp1.salary*0.02; for (int i=0;i<3;i++) { cout<<"enter an employee phone number ["<<i<<"] : "; cin>>emp1.phon_num[i]; } outf<<emp1.na.first<<"\t. 4 <<emp1.na.middle<<"\t" <<emp1.na.last<<"\t" <<emp1.bd.day<<"\t" <<emp1.bd.mon<<"\t" <<emp1.bd.year<<"\t" <<emp1.salary<<"\t" <<emp1.tax<<"\t" <<emp1.phon_num[0]<<"\t" <<emp1.phon_num[1]<<"\t" <<emp1.phon_num[2]<<"\n" ; cout<<"\n a new record has been added\n"; outf.close();

25 Struct in File (example). cout<<"\n **** the employee record is ****\n "<<endl; cout<<"\n employee name is : "<<emp1.na.first<<" " <<emp1.na.middle; cout<<" "<<emp1.na.last; cout<<"\n employee salary is : "<<emp1.salary; cout<<"\n employee tax is : "<<emp1.tax; cout<<"\n employee phone numbers are : "; for ( i=0;i<3;i++) cout<<emp1.phon_num[i]<<"\t"; cout<<"\n \n an employee birth date is : "; cout<<emp1.bd.day<< / "<<emp1.bd.mon<<" / "<<emp1.bd.year; cout<<endl<<endl; return 0; 25

26 Summary struct: collection of a fixed number of components Components can be of different types Called members Accessed by name struct is a reserved word No memory is allocated for a struct Memory when variables are declared 26

27 Summary (cont'd.) Dot (.) operator: member access operator Used to access members of a struct The only built-in operations on a struct are the assignment and member access Neither arithmetic nor relational operations are allowed on structs struct can be passed by value or reference A function can return a value of type struct structs can be members of other structs 27