Indexers and Classes
Indexers and Classes
Fundamentals of Indexed Properties and Classes
Introduction
Just as an indexed property can take a parameter of a primitive type, you can create an indexer that is of a class type. For example, you can create a class so that one of the its fields declared as an array can be accessed with an index directly applied to an instance of the class.
Practical Learning: Introducing Indexers and Classes
namespace PayrollPreparation7
{
public class Employee
{
public long EmployeeNumber { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public double HourlySalary { get; set; }
}
}using static System.Console;
namespace PayrollPreparation5
{
public class PayrollManagement
{
public static int Main(string[] args)
{
long emplNbr = 0L;
StaffManagement staff = new StaffManagement();
WriteLine(" Human Resources - Employees");
WriteLine("===========================================");
WriteLine("Empl # First Name Last Name Salary");
WriteLine("-------------------------------------------");
for (int i = 0; i < 5; i++)
WriteLine(" {0} {1} {2}{3}",
staff.pers[i].EmployeeNumber, staff.pers[i].FirstName,
staff.pers[i].LastName, staff.pers[i].HourlySalary);
WriteLine("===========================================");
try
{
Write("Enter an employee #: ");
emplNbr = long.Parse(ReadLine());
WriteLine("======================================");
WriteLine("Employee Details");
WriteLine("--------------------------------------");
WriteLine(staff[emplNbr]);
WriteLine("======================================");
}
catch (System.FormatException)
{
WriteLine("=- Invalid Employee Number -=");
}
return 0;
}
}
}namespace PayrollPreparation5
{
public class StaffManagement
{
public Employee[] pers;
public string this[long code]
{
get
{
for (int i = 0; i < pers.Length; i++)
if (code == pers[i].EmployeeNumber)
return "Employee #: " + pers[i].EmployeeNumber +
"\nFirst Name: " + pers[i].FirstName +
"\nLast Name: " + pers[i].LastName +
"\nHourly Salary: " + pers[i].HourlySalary.ToString("F");
return "Unidentifiable Employee";
}
}
public StaffManagement()
{
pers = new Employee[5];
pers[0] = new Employee();
pers[0].EmployeeNumber = 994_759;
pers[0].FirstName = "Michael ";
pers[0].LastName = "Grant ";
pers[0].HourlySalary = 22.58;
pers[1] = new Employee();
pers[1].EmployeeNumber = 394_225;
pers[1].FirstName = "Veronique ";
pers[1].LastName = "Beatten ";
pers[1].HourlySalary = 28.07;
pers[2] = new Employee();
pers[2].EmployeeNumber = 208_249;
pers[2].FirstName = "George ";
pers[2].LastName = "Kroll ";
pers[2].HourlySalary = 17.96;
pers[3] = new Employee();
pers[3].EmployeeNumber = 592_740;
pers[3].FirstName = "Maurissette";
pers[3].LastName = "Phukan ";
pers[3].HourlySalary = 30.05;
pers[4] = new Employee();
pers[4].EmployeeNumber = 379_725;
pers[4].FirstName = "Douglas ";
pers[4].LastName = "Sorrel ";
pers[4].HourlySalary = 26.37;
}
}
}using static System.Console;
namespace PayrollPreparation5
{
public class PayrollManagement
{
public static int Main(string[] args)
{
long emplNbr = 0L;
StaffManagement staff = new StaffManagement();
WriteLine(" Human Resources - Employees");
WriteLine("===========================================");
WriteLine("Empl # First Name Last Name Salary");
WriteLine("-------------------------------------------");
for (int i = 0; i < 5; i++)
WriteLine(" {0} {1} {2}{3}",
staff.pers[i].EmployeeNumber, staff.pers[i].FirstName,
staff.pers[i].LastName, staff.pers[i].HourlySalary);
WriteLine("===========================================");
try
{
Write("Enter an employee #: ");
emplNbr = long.Parse(ReadLine());
WriteLine("======================================");
WriteLine("Employee Details");
WriteLine("--------------------------------------");
WriteLine(staff[emplNbr]);
WriteLine("======================================");
}
catch (System.FormatException)
{
WriteLine("=- Invalid Employee Number -=");
}
return 0;
}
}
}Human Resources - Employees =========================================== Empl # First Name Last Name Salary ------------------------------------------- 994759 Michael Grant 22.58 394225 Veronique Beatten 28.07 208249 George Kroll 17.96 592740 Maurissette Phukan 30.05 379725 Douglas Sorrel 26.37 =========================================== Enter an employee #:
Human Resources - Employees =========================================== Empl # First Name Last Name Salary ------------------------------------------- 994759 Michael Grant 22.58 394225 Veronique Beatten 28.07 208249 George Kroll 17.96 592740 Maurissette Phukan 30.05 379725 Douglas Sorrel 26.37 =========================================== Enter an employee #: 994759 ====================================== Employee Details -------------------------------------- Employee #: 994759 First Name: Michael Last Name: Grant Hourly Salary: 22.58 ====================================== Press any key to continue . . .
An Integral Class-Based Indexed Property
Before designing an indexer that is class-based, first create the class that will be used as the data type. The class can be simple or complex as you judge it necessary. Here is an example of a simple class:
public class Student
{
public string FirstName { get; set; }
public string LastName { get; set; }
public int Gender { get; set; }
}
When creating the class that will host the indexed property, declare an array field for the class. Then, create the this property with the desired accessor(s). Here is an example:
public class Student
{
public string FirstName { get; set; }
public string LastName { get; set; }
public int Gender { get; set; }
}
public class SchoolRegistration
{
Student[] std = new Student[5];
public Student this[int i]
{
get { return std[i]; }
}
}
After creating the indexing class, you can use it and access the indexer. For example, you can retrieve its value(s). Here is an example:
using System;
public class Student
{
public string FirstName { get; set; }
public string LastName { get; set; }
public int Gender { get; set; }
}
public class SchoolRegistration
{
Student[] std = new Student[5];
public Student this[int i]
{
get { return std[i]; }
}
public SchoolRegistration()
{
std[0] = new Student();
std[0].FirstName = "Alfredo";
std[0].LastName = "Olmos";
std[0].Gender = 2;
std[1] = new Student();
std[1].FirstName = "Patricia";
std[1].LastName = "Katts";
std[1].Gender = 1;
std[2] = new Student();
std[2].FirstName = "Josiane";
std[2].LastName = "Euler";
std[2].Gender = 1;
std[3] = new Student();
std[3].FirstName = "Joan";
std[3].LastName = "Jones";
std[3].Gender = 3;
std[4] = new Student();
std[4].FirstName = "George";
std[4].LastName = "Paulson";
std[4].Gender = 2;
}
}
public class Exercise
{
static int Main(string[] args)
{
var pupils = new SchoolRegistration();
for (var i = 0; i < 5; i++)
{
Student pupil = pupils[i];
Console.WriteLine("Student Information");
Console.WriteLine("---------------------");
Console.WriteLine("First Name: {0}", pupil.FirstName);
Console.WriteLine("Last Name: {0}", pupil.LastName);
Console.WriteLine("Gender: {0}\n",
(pupil.Gender == 1 ? "Female" :
(pupil.Gender == 2 ? "Male" : "Unknown")));
}
return 0;
}
}
This would produce:
Student Information --------------------- First Name: Alfredo Last Name: Olmos Gender: Male Student Information --------------------- First Name: Patricia Last Name: Katts Gender: Female Student Information --------------------- First Name: Josiane Last Name: Euler Gender: Female Student Information --------------------- First Name: Joan Last Name: Jones Gender: Unknown Student Information --------------------- First Name: George Last Name: Paulson Gender: Male Press any key to continue . . .
Practical Learning: Using an Integer-Based Indexer
namespace PayrollPreparation5
{
public class StaffManagement
{
public Employee[] pers;
public Employee this[int i]
{
get
{
return pers[i];
}
}
public StaffManagement()
{
pers = new Employee[5];
pers[0] = new Employee();
pers[0].EmployeeNumber = 994_759;
pers[0].FirstName = "Michael ";
pers[0].LastName = "Grant ";
pers[0].HourlySalary = 22.58;
pers[1] = new Employee();
pers[1].EmployeeNumber = 394_225;
pers[1].FirstName = "Veronique ";
pers[1].LastName = "Beatten ";
pers[1].HourlySalary = 28.07;
pers[2] = new Employee();
pers[2].EmployeeNumber = 208_249;
pers[2].FirstName = "George ";
pers[2].LastName = "Kroll ";
pers[2].HourlySalary = 17.96;
pers[3] = new Employee();
pers[3].EmployeeNumber = 592_740;
pers[3].FirstName = "Maurissette";
pers[3].LastName = "Phukan ";
pers[3].HourlySalary = 30.05;
pers[4] = new Employee();
pers[4].EmployeeNumber = 379_725;
pers[4].FirstName = "Douglas ";
pers[4].LastName = "Sorrel ";
pers[4].HourlySalary = 26.37;
}
}
}using static System.Console;
namespace PayrollPreparation5
{
public class PayrollManagement
{
public static int Main(string[] args)
{
StaffManagement staff = new StaffManagement();
WriteLine(" Human Resources - Employees");
WriteLine("===========================================");
WriteLine("Empl # First Name Last Name Salary");
WriteLine("-------------------------------------------");
for (int i = 0; i < 5; i++)
{
Employee clerk = staff[i];
WriteLine(" {0} {1} {2}{3}",
clerk.EmployeeNumber, clerk.FirstName,
clerk.LastName, clerk.HourlySalary);
}
WriteLine("===========================================");
return 0;
}
}
}Human Resources - Employees =========================================== Empl # First Name Last Name Salary ------------------------------------------- 994759 Michael Grant 22.58 394225 Veronique Beatten 28.07 208249 George Kroll 17.96 592740 Maurissette Phukan 30.05 379725 Douglas Sorrel 26.37 =========================================== Press any key to continue . . .
namespace PayrollPreparation5
{
public class Employee
{
public long EmployeeNumber { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public double HourlySalary { get; set; }
public override string ToString()
{
return $"Employee #: {EmployeeNumber}\n" +
$"First Name: {FirstName}\n" +
$"Last Name: {LastName}\n" +
$"Hourly Salary: {HourlySalary}";
}
}
}An Indexed Property Using Another Primitive Type
As done for primitive types, an indexer can take a parameter other than an integer. In some cases, you may use your class or a class created by someone else and need to access an element of the array without information other than its index. Consider the following program:
public enum Classification
{
Female,
Male,
Unknown
}
public class Student
{
public long StudentID { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public Classification Gender;
public override string ToString()
{
string str = "Student ID: " + StudentID +
"\nFirst Name: " + firstName +
"\nLast Name: " + lastName +
"\nGender: " + Gender;
return str;
}
}
public class SchoolRegistration
{
Student[] std = new Student[50];
public Student this[...]
{
}
}
Previously, we saw that you could create an indexer that takes a type than an integer. For example, we saw that a string could be used as an index.
By now, we know that a basic indexed property produces (or all the indexed properties we have studied so far produce) only one value. If you have a class that has only one field or property, this would be enough. In reality, most of the time, a class has many fields and/or properties. In such a case, when you create an indexer , you need to be able to refer to one exact element of the array. To make this possible, you must define a way to point to the particular element you want. One way you can do this is to use one field of the class as a reference. This is better if that field holds unique values among the other elements of the array. For our Student class, we could use the StudentID field (because we will make sure that each student has a unique ID). You can start the property as follows:
public class SchoolRegistration
{
Student[] std = new Student[5];
public Student this[long id]
{
}
}
When a user uses this property, he or she must provide a value that uniquely identifies an element of the array. You in turn, when you get this value, you can search for it in the array. If you find it and the array has a get accessor, you can then return the desired but appropriate value. Here is how this can be done:
public class SchoolRegistration
{
Student[] students = new Student[50];
public Student this[long id]
{
get
{
for (int i = 0; i < students.Length; i++)
{
if (students[i].StudentID == id)
return students[i];
}
// Unknown student or the number was not found
return null;
}
}
}
After creating the indexer, you can use it. Once again, you must follow the rules of a method that takes an argument and returns a value other than void. In this case, the indexer must take a string and it must return a Student object. Here is an example:
using System;
public enum Classification
{
Female,
Male,
Unknown
}
public class Student
{
public long StudentID { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public Classification Gender { get; set; }
public override string ToString()
{
string str = "Student ID: " + StudentID +
"\nFirst Name: " + FirstName +
"\nLast Name: " + LastName +
"\nGender: " + Gender;
return str;
}
}
public class SchoolRegistration
{
Student[] students = new Student[50];
public Student this[long id]
{
get
{
for (int i = 0; i < students.Length; i++)
{
if (students[i].StudentID == id)
return students[i];
}
// Unknown student or the number was not found
return null;
}
}
public SchoolRegistration()
{
students[0] = new Student();
students[0].StudentID = 917294;
students[0].FirstName = "Gabrielle";
students[0].LastName = "Mukoko";
students[0].Gender = Classification.Female;
students[1] = new Student();
students[1].StudentID = 283764;
students[1].FirstName = "Patrick";
students[1].LastName = "Katts";
students[1].Gender = Classification.Unknown;
students[2] = new Student();
students[2].StudentID = 192046;
students[2].FirstName = "Armand";
students[2].LastName = "Essono";
students[2].Gender = Classification.Male;
students[3] = new Student();
students[3].StudentID = 618268;
students[3].FirstName = "Bertrand";
students[3].LastName = "Wenger";
students[3].Gender = Classification.Male;
students[4] = new Student();
students[4].StudentID = 820648;
students[4].FirstName = "Hortense";
students[4].LastName = "McNeal";
students[4].Gender = Classification.Female;
}
}
public class Exercise
{
static int Main(string[] args)
{
var pupils = new SchoolRegistration();
var pupil = pupils[820648];
Console.WriteLine("Student Information");
Console.WriteLine("---------------------");
Console.WriteLine("First Name: {0}", pupil.FirstName);
Console.WriteLine("Last Name: {0}", pupil.LastName);
Console.WriteLine("Gender: {0}\n", pupil.Gender);
pupil = pupils[192046];
Console.WriteLine("Student Information");
Console.WriteLine("---------------------");
Console.WriteLine("First Name: {0}", pupil.FirstName);
Console.WriteLine("Last Name: {0}", pupil.LastName);
Console.WriteLine("Gender: {0}\n", pupil.Gender);
return 0;
}
}
This would produce:
Student Information --------------------- First Name: Hortense Last Name: McNeal Gender: Female Student Information --------------------- First Name: Armand Last Name: Essono Gender: Male Press any key to continue . . .
Topics on Indexed Properties and Classes
A Class as Index
As opposed to returning a class, an indexer can use a class as its index. When creating such a property, the primary action you must take is to include a class and its name as a parameter to the this property. You can start such a class as follows:
using System;
public enum Classification
{
Female,
Male,
Unknown
}
public class Student
{
public long StudentID { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public Classification Gender { get; set; }
}
public class SchoolRegistration
{
public string this[Student std]
{
}
}
When implementing the class, you should proceed the same way we have done so far following the rules of a method that takes an argument and returns a value other than void. Here is an example:
public class SchoolRegistration
{
Student[] students = new Student[50];
public string this[Student std]
{
get
{
for (int i = 0; i < students.Length; i++)
{
if (std.StudentID == students[i].StudentID)
return "Student ID: " + students[i].StudentID +
"\nFirst Name: " + students[i].FirstName +
"\nLast Name: " + students[i].LastName +
"\nGender: " + students[i].Gender;
}
// Unknown student or the number was not found
return "";
}
}
}
After creating the property, you can use it. To do this, you must pass an object that is the type of the index. You can then use the returned value as you see fit. Here is an example:
using System;
public enum Classification
{
Female,
Male,
Unknown
}
public class Student
{
public long StudentID { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public Classification Gender { get; set; }
}
public class SchoolRegistration
{
Student[] students = new Student[50];
public string this[Student std]
{
get
{
for (int i = 0; i < students.Length; i++)
{
if (std.StudentID == students[i].StudentID)
return "Student ID: " + students[i].StudentID +
"\nFirst Name: " + students[i].FirstName +
"\nLast Name: " + students[i].LastName +
"\nGender: " + students[i].Gender;
}
// Unknown student or the number was not found
return "";
}
}
public SchoolRegistration()
{
students[0] = new Student();
students[0].StudentID = 917294;
students[0].FirstName = "Gabrielle";
students[0].LastName = "Mukoko";
students[0].Gender = Classification.Female;
students[1] = new Student();
students[1].StudentID = 283764;
students[1].FirstName = "Patrick";
students[1].LastName = "Katts";
students[1].Gender = Classification.Unknown;
students[2] = new Student();
students[2].StudentID = 192046;
students[2].FirstName = "Armand";
students[2].LastName = "Essono";
students[2].Gender = Classification.Male;
students[3] = new Student();
students[3].StudentID = 618268;
students[3].FirstName = "Bertrand";
students[3].LastName = "Wenger";
students[3].Gender = Classification.Male;
students[4] = new Student();
students[4].StudentID = 820648;
students[4].FirstName = "Hortense";
students[4].LastName = "McNeal";
students[4].Gender = Classification.Female;
students[5] = new Student();
students[5].StudentID = 917394;
students[5].FirstName = "Alfredo";
students[5].LastName = "Olmos";
students[5].Gender = Classification.Unknown;
students[6] = new Student();
students[6].StudentID = 163864;
students[6].FirstName = "Josiane";
students[6].LastName = "Euler";
students[6].Gender = Classification.Female;
students[7] = new Student();
students[7].StudentID = 826384;
students[7].FirstName = "Joan";
students[7].LastName = "Jones";
students[7].Gender = Classification.Female ;
}
}
public class Exercise
{
static int Main(string[] args)
{
var pupils = new SchoolRegistration();
var pupil = new Student();
pupil.StudentID = 820648;
var strStudent = pupils[pupil];
Console.WriteLine("=====================");
Console.WriteLine("Student Information");
Console.WriteLine("---------------------");
Console.WriteLine(strStudent);
//pupil = new Student();
pupil.StudentID = 192046;
strStudent = pupils[pupil];
Console.WriteLine("=====================");
Console.WriteLine("Student Information");
Console.WriteLine("---------------------");
Console.WriteLine(strStudent);
Console.WriteLine("=====================\n");
return 0;
}
}
This would produce:
===================== Student Information --------------------- Student ID: 820648 First Name: Hortense Last Name: McNeal Gender: Female ===================== Student Information --------------------- Student ID: 192046 First Name: Armand Last Name: Essono Gender: Male ===================== Press any key to continue . . .
You can also directly pass an instance of the class in the square brackets of the object that holds the indexed property, as long as you specify the object. Here is an example:
using System;
public enum Classification
{
Female,
Male,
Unknown
}
public class Student
{
public long StudentID { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public Classification Gender { get; set; }
public Student()
{
}
public Student(long id)
{
this.StudentID = id;
}
}
public class SchoolRegistration
{
Student[] students = new Student[50];
public string this[Student std]
{
. . . No Change
}
public SchoolRegistration()
{
. . . No Change
}
}
public class Exercise
{
static int Main(string[] args)
{
var pupils = new SchoolRegistration();
var strStudent = pupils[new Student(618268)];
Console.WriteLine("=====================");
Console.WriteLine("Student Information");
Console.WriteLine("---------------------");
Console.WriteLine(strStudent);
Console.WriteLine("=====================\n");
return 0;
}
}
This would produce:
===================== Student Information --------------------- Student ID: 618268 First Name: Bertrand Last Name: Wenger Gender: Male ===================== Press any key to continue . . .
Overloading a Class-Based Indexed Property
As mentioned for indexers that return primitive types, you can overload an indexed property that produces a class. You do this following the same rules applied to method overloading and arrays:
using System;
public enum Classification
{
Female,
Male,
Unknown
}
public class Major
{
public string Name;
public int CreditsRequired;
}
public class Student
{
public long StudentNumber;
public string FullName;
public Classification Gender;
public override string ToString()
{
string str = "Student #: " + StudentNumber.ToString() +
"\nFull Name: " + FullName +
"\nGender: " + Gender;
return str;
}
}
public class StudentRegistration
{
private Student[] std = new Student[5];
public StudentRegistration()
{
std[0] = new Student();
std[0].StudentNumber = 304850;
std[0].FullName = "Gabrielle Mukoko";
std[0].Gender = Classification.Female;
std[1] = new Student();
std[1].StudentNumber = 926304;
std[1].FullName = "Patrick Katts";
std[1].Gender = Classification.Unknown;
std[2] = new Student();
std[2].StudentNumber = 330647;
std[2].FullName = "Armand Essono";
std[2].Gender = Classification.Male;
std[3] = new Student();
std[3].StudentNumber = 631846;
std[3].FullName = "Bertrand Wenger";
std[3].Gender = Classification.Male;
std[4] = new Student();
std[4].StudentNumber = 209374;
std[4].FullName = "Anselme Bongos";
std[4].Gender = Classification.Male;
}
// This property takes a string and produces a Student object
public Student this[string strFullName]
{
get
{
for (int i = 0; i < std.Length; i++)
{
if (std[i].FullName == strFullName)
return std[i];
}
return null;
}
}
// This property takes a number and produces a Student object
public Student this[long nbr]
{
get
{
for (int i = 0; i < std.Length; i++)
{
if( nbr == std[i].StudentNumber )
return std[i];
}
return null;
}
}
// This property takes a major produces its definition
public string this[Major maj]
{
get
{
return "Major: " + maj.Name +
" - " + maj.CreditsRequired +
" Credits Required";
}
}
}
public class Exercise
{
static int Main(string[] args)
{
var pupils = new StudentRegistration();
var m1 = new Major();
m1.Name = "Computer Sciences";
m1.CreditsRequired = 120;
var m2 = new Major();
m2.Name = "Informtation Technology";
m2.CreditsRequired = 120;
Console.WriteLine("=-= Student Identification =-=");
Console.WriteLine(pupils["Gabrielle Mukoko"]);
Console.WriteLine(pupils[m1]);
Console.WriteLine("--------------------------------------------------");
Console.WriteLine("=-= Student Identification =-=");
Console.WriteLine(pupils[330647]);
Console.WriteLine(pupils[m2]);
Console.WriteLine("--------------------------------------------------");
Console.WriteLine();
return 0;
}
}
This would produce:
=-= Student Identification =-= Student #: 304850 Full Name: Gabrielle Mukoko Gender: Female Major: Computer Sciences - 120 Credits Required -------------------------------------------------- =-= Student Identification =-= Student #: 330647 Full Name: Armand Essono Gender: Male Major: Information Technology - 120 Credits Required -------------------------------------------------- Press any key to continue . . .
using System;
public enum Classification
{
Female,
Male,
Unknown
}
public class Student
{
public long StudentID { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public Classification Gender { get; set; }
public Student()
{
}
public Student(long id)
{
this.StudentID = id;
}
public override string ToString()
{
return "Student ID: " + StudentID +
"\nFirst Name: " + FirstName +
"\nLast Name: " + LastName +
"\nGender: " + Gender;
}
}
public enum CourseDelivery
{
FaceToFace,
Online,
Both // Student Choose
}
public class Course
{
public string ShortName;
public string LongName;
public string Description;
public int Credits;
public CourseDelivery DeliveryMode;
public Course()
{
}
public Course(string name)
{
ShortName = name;
}
public override string ToString()
{
return "Course: " + ShortName +
"\nFull Name: " + LongName +
"\nCredits: " + Credits +
"\nDescription: " + Description +
"\nDelivery: " + DeliveryMode;
}
}
public class SchoolRegistration
{
Student[] students = new Student[50];
Course[] classes = new Course[3];
// This indexer takes a student id and
// returns the student information
public Student this[long id]
{
get
{
for (int i = 0; i < students.Length; i++)
{
if (id == students[i].StudentID)
return students[i];
}
// Unknown student or the number was not found
return null;
}
}
// This indexer takes a course short name and
// it produces a summary of the course information
public Course this[string name]
{
get
{
for (int i = 0; i < classes.Length; i++)
{
if (name == classes[i].ShortName)
return classes[i];
}
// Unknown course
return null;
}
}
public string this[Course ToAttend, Student registrant]
{
get
{
// First check that the class exists
for (int i = 0; i < classes.Length; i++)
{
if (ToAttend.ShortName == classes[i].ShortName)
{
// If the class exists, then check if the student exists
for (int j = 0; j < students.Length; j++)
{
if (registrant.StudentID == students[j].StudentID)
{
return "Student Identification --\n " +
"Student ID: " +
students[j].StudentID +
"\n Full Name: " + students[j].LastName +
", " + students[j].FirstName +
"\nClass to Attend --\n Course: " +
classes[i].ShortName + " - " +
classes[i].LongName + " (" +
classes[i].Credits + ")" +
"\n Delivery: " +
classes[i].DeliveryMode;
}
}
}
}
return "Invalid Registration - You may have to start over";
}
}
// This property takes information used to register
// a student to a course
// It also specifies whether the student is willing
// to get in the waiting list in case another students drops out
public string this[Student stud, Course Class, bool WaitingList]
{
get
{
// Check that the student information is valie
for (int j = 0; j < students.Length; j++)
{
if (stud.StudentID == students[j].StudentID)
{
// Now that the student information has been found,
// check if the course information is correct
for (int i = 0; i < classes.Length; i++)
{
if (Class.ShortName == classes[i].ShortName)
{
// If the class exists, then check
// if the student exists
return "Student Identification --\n " +
"Student ID: " +
students[j].StudentID +
"\n Full Name: " + students[j].LastName +
", " + students[j].FirstName +
"\nClass to Attend --\n Course: " +
classes[i].ShortName + " - " +
classes[i].LongName + " (" +
classes[i].Credits + ")" +
"\n Delivery: " +
classes[i].DeliveryMode +
"\nStudent is willing to get " +
"on the waiting list: "
+ WaitingList;
}
}
}
}
return "Invalid Registration - You may have to start over";
}
}
public SchoolRegistration()
{
students[0] = new Student();
students[0].StudentID = 917294;
students[0].FirstName = "Gabrielle";
students[0].LastName = "Mukoko";
students[0].Gender = Classification.Female;
students[1] = new Student();
students[1].StudentID = 283764;
students[1].FirstName = "Patrick";
students[1].LastName = "Katts";
students[1].Gender = Classification.Unknown;
students[2] = new Student();
students[2].StudentID = 192046;
students[2].FirstName = "Armand";
students[2].LastName = "Essono";
students[2].Gender = Classification.Male;
students[3] = new Student();
students[3].StudentID = 618268;
students[3].FirstName = "Bertrand";
students[3].LastName = "Wenger";
students[3].Gender = Classification.Male;
students[4] = new Student();
students[4].StudentID = 820648;
students[4].FirstName = "Hortense";
students[4].LastName = "McNeal";
students[4].Gender = Classification.Female;
classes[0] = new Course();
classes[0].ShortName = "PHIL140";
classes[0].LongName = "Philosophy - Contemporary Moral Issues";
classes[0].Credits = 3;
classes[0].Description = "An exploration of how " +
"philosophical analysis can be " +
"\n\t\ta foundation for thinking " +
"clearly about moral issues. " +
"\n\t\tProblems analyzed include such " +
"widely debated issues " +
"\n\t\tas abortion, euthanasia, " +
"the death penalty, " +
"\n\t\thomosexuality, pornography, " +
"reverse discrimination, " +
"\n\t\tbusiness ethics, sexual " +
"equality, and economic equity.";
classes[1] = new Course();
classes[1].ShortName = "MATH140";
classes[1].LongName = "Calculus I";
classes[1].Credits = 4;
classes[1].Description = "An introduction to calculus. " +
"Topics include functions, " +
"\n\t\tthe sketching of graphs of " +
"functions, limits, continuity, " +
"\n\t\tderivatives and applications of " +
"the derivative, definite " +
"\n\t\tand indefinite integrals, " +
"and calculation of area.";
classes[2] = new Course();
classes[2].ShortName = "ASTR100";
classes[2].LongName = "Introduction to Astronomy";
classes[2].Credits = 3;
classes[2].Description = "A discussion of the major areas " +
"of astronomy. Topics " +
"\n\t\tinclude the solar system, " +
"stars and stellar evolution, " +
"\n\t\tand galaxies. Current topics " +
"in astronomy are also " +
"\n\t\tdiscussed.";
}
}
public class Exercise
{
static int Main(string[] args)
{
var pupils = new SchoolRegistration();
Student std = new Student(917294);
Course crs = new Course("MATH140");
Console.WriteLine("================================================");
Console.WriteLine("Student Registration");
Console.WriteLine("------------------------------------------");
Console.WriteLine(pupils[crs, std]);
std = new Student(820648);
crs = new Course("PHIL140");
Console.WriteLine("================================================");
Console.WriteLine("Student Registration");
Console.WriteLine("------------------------------------------");
Console.WriteLine(pupils[std, crs, true]);
Console.WriteLine("================================================\n");
return 0;
}
}
This would produce:
================================================ Student Registration ------------------------------------------ Student Identification -- Student ID: 917294 Full Name: Mukoko, Gabrielle Class to Attend -- Course: MATH140 - Calculus I (4) Delivery: FaceToFace ================================================ Student Registration ------------------------------------------ Student Identification -- Student ID: 820648 Full Name: McNeal, Hortense Class to Attend -- Course: PHIL140 - Philosophy - Contemporary Moral Issues (3) Delivery: FaceToFace Student is willing to get on the waiting list: True ================================================ Press any key to continue . . .
Practical Learning: Overloading an Indexer
namespace PayrollPreparation5
{
public class StaffManagement
{
public Employee[] pers;
public Employee this[int i]
{
get
{
if((i >= 0) && (i < pers.Length))
return pers[i];
throw null;
}
}
public Employee this[long nbr]
{
get
{
for(int i = 0; i < pers.Length; i++)
if (nbr == pers[i].EmployeeNumber)
return pers[i];
return null;
}
}
public StaffManagement()
{
pers = new Employee[5];
pers[0] = new Employee();
pers[0].EmployeeNumber = 994_759;
pers[0].FirstName = "Michael ";
pers[0].LastName = "Grant ";
pers[0].HourlySalary = 22.58;
pers[1] = new Employee();
pers[1].EmployeeNumber = 394_225;
pers[1].FirstName = "Veronique ";
pers[1].LastName = "Beatten ";
pers[1].HourlySalary = 28.07;
pers[2] = new Employee();
pers[2].EmployeeNumber = 208_249;
pers[2].FirstName = "George ";
pers[2].LastName = "Kroll ";
pers[2].HourlySalary = 17.96;
pers[3] = new Employee();
pers[3].EmployeeNumber = 592_740;
pers[3].FirstName = "Maurissette";
pers[3].LastName = "Phukan ";
pers[3].HourlySalary = 30.05;
pers[4] = new Employee();
pers[4].EmployeeNumber = 379_725;
pers[4].FirstName = "Douglas ";
pers[4].LastName = "Sorrel ";
pers[4].HourlySalary = 26.37;
}
}
}using static System.Console;
namespace PayrollPreparation5
{
public class PayrollManagement
{
public static int Main(string[] args)
{
long emplNbr = 0L;
StaffManagement staff = new StaffManagement();
WriteLine(" Human Resources - Employees");
WriteLine("===========================================");
WriteLine("Empl # First Name Last Name Salary");
WriteLine("-------------------------------------------");
for (int i = 0; i < 5; i++)
{
Employee clerk = staff[i];
WriteLine(" {0} {1} {2}{3}",
clerk.EmployeeNumber, clerk.FirstName,
clerk.LastName, clerk.HourlySalary);
}
WriteLine("===========================================");
try
{
Write("Enter an employee #: ");
emplNbr = long.Parse(ReadLine());
WriteLine("======================================");
WriteLine("Employee Details");
WriteLine("--------------------------------------");
WriteLine(staff[emplNbr]);
WriteLine("======================================");
}
catch (System.FormatException)
{
WriteLine("=- Invalid Employee Number -=");
}
return 0;
}
}
}Human Resources - Employees =========================================== Empl # First Name Last Name Salary ------------------------------------------- 994759 Michael Grant 22.58 394225 Veronique Beatten 28.07 208249 George Kroll 17.96 592740 Maurissette Phukan 30.05 379725 Douglas Sorrel 26.37 =========================================== Enter an employee #: 208249 ====================================== Employee Details -------------------------------------- Employee #: 208249 First Name: George Last Name: Kroll Hourly Salary: 17.96 ====================================== Press any key to continue . . .
Read/Write Indexed Properties
As done for a primitive type, you can allow the clients of your indexer to assign values to the array's elements. Once again, when defining the property, you should include a set accessor to it. In the set accessor, you should assign the value keyword to an element of the array. Here is an example:
public class SchoolRegistration
{
Student[] std = new Student[5];
public Student this[int i]
{
get { return std[i]; }
set { std[i] = value; }
}
}
After doing this, you can create an element of the array by applying the square brackets to the instance of the class and assigning the desired value to it. The problem with the class is that, since it may have many fields (or properties), to completely define each element, you must provide a value to the member variables of the class itself. Here is an example:
using System;
public enum Classification
{
Female,
Male,
Unknown
}
public class Student
{
public long StudentID { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public Classification Gender { get; set; }
public override string ToString()
{
string str = "Student ID: " + StudentID +
"\nFirst Name: " + FirstName +
"\nLast Name: " + LastName +
"\nGender: " + Gender;
return str;
}
}
public class SchoolRegistration
{
Student[] std = new Student[5];
public Student this[int i]
{
get { return std[i]; }
set { std[i] = value; }
}
}
public class Exercise
{
static int Main(string[] args)
{
var registration = new SchoolRegistration();
var stud = new Student();
stud.StudentID = 604057;
stud.FirstName = "Gertrude";
stud.LastName = "Monayong";
stud.Gender = Classification.Female;
registration[2] = stud;
Console.WriteLine("Student Information");
Console.WriteLine("---------------------");
Console.WriteLine("First Name: {0}", registration[2].FirstName);
Console.WriteLine("Last Name: {0}", registration[2].LastName);
Console.WriteLine("Gender: {0}\n",registration[2].Gender);
return 0;
}
}
This would produce:
Student Information --------------------- First Name: Gertrude Last Name: Monayong Gender: Female Press any key to continue . . .
Practical Learning: Ending the Lesson
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