1. CS 1430: Programming in C++

2. Class Student class Student { private: string id;
string firstName, lastName;
float gpa;
public:
void Read()
. . .
void Write()
float GetGPA()
void SetGPA( float value )
void UpdateGPA( float amount ) };
// Student is a data type
// Data and functions together

3. Class and Object // Declare variable and reserve memory space
int numStudents;
// Declare class variable
// memory space for data fields
// methods
Student s1;
// Input data into object s1
s1.Read();
// No values for data members
s1.Write();

4. Use Class Constructors!
Initial Values
// Declare variable with initial value
int numStudents = 0;
// Can we declare class variable with initial value?
Student s1;
Use Class Constructors!

5. Class Default Constructor
class Student {
private:
string id;
string firstName, lastName;
float gpa;
public:
Student()
id = “12345”;
firstName = “first”;
lastName = “last”;
gpa = 0.0; } };
// Syntax for constructor
// Default constructor has no parameters

6. Default Class Constructor
// Default constructor is called
Student s1;
// The default constructor has set the
// values for data members
s1.Write();
// This will change the data fields
s1.Read();
// Output data of object s1
Default Constructor is called implicitly when class variables are declared.

7. Class Default Constructor
class Student {
private:
string id;
string firstName, lastName;
float gpa;
public:
Student()
id = “”;
firstName = “”;
lastName = “”;
gpa = 0.0; } };
// Empty strings and zero: special values.
// Not garbage!

8. Constructor with Parameters
class Student {
private:
string id;
string firstName, lastName;
float gpa;
public:
Student(string sID, string first, string last, float g)
id = sID;
firstName = first;
lastName = last;
gpa = g; } };

9. Constructor with Parameters
// Class constructor is called
Student s1(“12345”, “John”, “Smith”, 2.8);
// The constructor has set the
// values for data members
s1.Write();
// This will change gpa
s1.UpdateGPA(0.1);
// Output data of object s1

10. Class Constructors with Different Parameters
class Student {
private:
. . .
public:
Student(string sID)
id = sID;
// could set other default values }
Student(string first, string last)
firstName = first;
lastName = last;
gpa = 0.0; // can set gpa with a default value };

11. Class Constructors // Student(string sID) is called
// Student(string first, string last) is called
Student s2(“Qi”, “Yang”);
// Student(String sID, string first, string last,
// float g) is called
Student s3(“13579”, “Joe”, “Clifton”, 3.9);
// Student() is called
Student s4();

12. Different Constructors Must Have Different Parameters
class Student {
private:
. . .
public:
Student(string last, string first)
firstName = first;
lastName = last; }
Student(string first, string last) };
Will this work?

13. Different Constructors Must Have Different Parameters
// Which one will be called?
// Student(string first, string last)
// Student(string last, string first)
Student s(“Qi”, “Yang”);

14. Different Parameters: Different Type
class Student {
private:
. . .
public:
Student(string last, string first)
firstName = first;
lastName = last; }
Student(string sID, float g)
id = sID;
gpa = g; };

15. Different Parameters: Different Type
// Student(string first, string last) is called
Student s(“Qi”, “Yang”);
// Student(string sID, float g) is called
Student s(“12345”, 3.3);

16. Class Constructors class Student { private: . . . public: Student()
Student(string sID)
Student(string first, string last)
Student(string sID, float g)
Student(string sID, string first, string last, float g) };

17. Class Constructors // Student(string sID) is called
// Student(string first, string last) is called
Student s2(“Qi”, “Yang”);
// Student(String sID, string first, string last,
// float g) is called
Student s3(“13579”, “Joe”, “Clifton”, 3.9);
// Student() is called
Student s4();
// Student(string sID, float g) is called
Student s(“12345”, 3.3);

18. No Default Constructor
class Student {
private:
. . .
public:
// Student()
Student(string sID)
Student(string first, string last)
Student(string sID, float g)
Student(string sID, string first, string last, float g) };

19. No Default Constructor
// Student(string sID) is called
Student s1(“56789”);
// Student(string first, string last) is called
Student s2(“Qi”, “Yang”);
// Student(String sID, string first, string last,
// float g) is called
Student s3(“13579”, “Joe”, “Clifton”, 3.9);
// Student(string sID, float g) is called
Student s(“12345”, 3.3);
// No default constructor if a constructor is defined.
Student s4(); // Invalid!

20. No Constructors class Student { private: . . . public: /* Student()
Student(string sID)
Student(string first, string last)
Student(string sID, float g)
Student(string sID, string first, string last, float g) */ };

21. Class Constructors // Invalid Student s1(“56789”);
Student s2(“Qi”, “Yang”);
Student s3(“13579”, “Joe”, “Clifton”, 3.9);
Student s(“12345”, 3.3);
// Default constructor is good!
Student s4();
// Will not work!
s4.Write();
s4.UpdateGPA( 0.1 );

22. // --------------------------------------------------
// Each class must have a comment block
// to describe it.
class Student {
private:
string id;
string firstName, lastName;
float gpa;
public:
// constructors
Student()
. . .
Student(string sID, string first, string last)
// methods
void Read()
void Write()
float GetGPA() };

23. class Student {
private:
string id, firstName, lastName;
float gpa;
// Why do we need it?
// Can we do this?
// What is this?
Student (string sID)
id = sID; }
public:
// constructors
Student()
. . .
Student(string sID, string first, string last)
// methods
void WhatMethod(. . .) };

24. class Student {
private:
string id, firstName, lastName;
float gpa;
// private constructor
Student (string sID)
. . .
// private method
// what is this?
int WhatToDo()
public:
// constructors
Student()
Student(string sID, string first, string last)
// methods
void WhatMethod(. . .) };

25. class Student {
private:
string id, firstName, lastName;
float gpa;
Student (string sID)
int WhatToDo()
public:
Student()
Student(string sID, string first, string last)
// methods
void WhatMethod()
void Read()
void Write()
string GetFirst()
float getGPA()
void setGPA( float value )
void updateGPA( float amount ) };

26. class Student {
private:
. . .
int WhatToDo()
public:
void WhatMethod() };
int main()
Student s1, s2;
s1.Read();
s1.Write();
s1.SetGPA(3.1);
s1.WhatMethod(); // valid?
s1.WhatToDo(); // valid?
return 0; }

27. class Student {
. . . };
int main()
Student s1, s2;
s1.Read();
s1.Write();
Student s3(“Qi”, “Yang”, “1418”);
s3.SetGPA(3.1);
s2 = s3; // valid?
s2.Write();
if (s1 > s2) // valid?
cout << “Student ” << s1.GetFirst() << “ is better than ”
<< s2.GetFirst() << ‘.’;
return 0; }

28. class Student {
. . . };
int main()
Student s1, s2;
s1.Read();
s1.Write();
Student s3(“Qi”, “Yang”, “1418”);
s3.SetGPA(3.1);
s2 = s3; // Good! Copy all fields.
s2.Write();
if (s1 > s2) // Invalid!
cout << “Student ” << s1.GetFirst() << “ is better than ”
<< s2.GetFirst() << ‘.’;
return 0; }

29. class Student {
. . . };
int main()
Student s1, s2;
Student s3(“Qi”, “Yang”, “1418”);
s3.SetGPA(3.1);
s2 = s3; // Good! Copy all fields.
if (s1.GetGPA() > s2.GetGPA()) // Valid!
cout << “Student ” << s1.GetFirst() << “ is better than ”
<< s2.GetFirst() << ‘.’;
cin >> s1; // Valid?
cout << s1; // Valid?
return 0; }

30. Schedule
Quiz7-2: Due Monday
Program 4
Lab8
Test 2

31. Prog4 Five required functions You can make additional functions
Follow the Programming Rules