Date post: | 18-Jan-2016 |
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Class Studentclass Student
{
private:
string id;
string firstName, lastName;
float gpa;
public:
void Read()
void Write()
string getGPA()
void setGPA( float value )
void updateGPA( float amount )
. . .
};
// Student is a data type
// Data and functions together1
Class and Object
// Declare variable and reserve memory spaceint numStudents;
// Declare class variable// memory space for data fields// methodsStudent s1;
// Input data into object s1s1.Read();
// No values for data memberss1.Write();
2
Initial Values
// Declare variable with initial valueint numStudents = 0;
// Can we declare class variable with initial value?Student s1;
Use Class Constructors!
3
Class Default Constructorclass Student
{
private:
string id;
string firstName, lastName;
float gpa;
public:
Student()
{
id = “12345”;
firstName = “first”;
lastName = “last”;
gpa = 2.5;
}
};
// Syntax for constructor
// Default constructor has no parameters4
Default Class Constructor
// Default constructor is calledStudent s1;
// The default constructor has set the // values for data memberss1.Write();
// This will change the data fieldss1.Read();
// Output data of object s1s1.Write();
Constructor is called implicitly when class variables are declared.
5
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;
}
};
6
Constructor with Parameters
// Class constructor is calledStudent s1(“12345”, “John”, “Smith”, 2.8);
// The constructor has set the // values for data memberss1.Write();
// This will change gpas1.UpdateGPA(0.1);
// Output data of object s1s1.Write();
7
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 = 2.5; // can still set gpa
}
};8
Class Constructors
// Student(string sID) is calledStudent s1(“56789”);
// Student(string first, string last) is calledStudent s2(“Qi”, “Yang”);
// Student(String sID, string first, string last, // float g) is calledStudent s3(“13579”, “Joe”, “Clifton”, 3.9);
// Student() is calledStudent s4();
9
Different Constructors Must Have Different Parameters
class Student
{
private:
. . .
public:
Student(string last, string first)
{
firstName = first;
lastName = last;
}
Student(string first, string last)
{
firstName = first;
lastName = last;
}
};
Will this work?10
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”);
11
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;
}
};12
Different Parameters:Different Type
// Student(string first, string last) is calledStudent s(“Qi”, “Yang”);
// Student(string sID, float g) is calledStudent s(“12345”, 3.3);
13
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)
};
14
Class Constructors
// Student(string sID) is calledStudent s1(“56789”);
// Student(string first, string last) is calledStudent s2(“Qi”, “Yang”);
// Student(String sID, string first, string last, // float g) is calledStudent s3(“13579”, “Joe”, “Clifton”, 3.9);
// Student() is calledStudent s4();
// Student(string sID, float g) is calledStudent s(“12345”, 3.3);
15
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)
};
16
No Default Constructor
// Student(string sID) is calledStudent s1(“56789”);
// Student(string first, string last) is calledStudent s2(“Qi”, “Yang”);
// Student(String sID, string first, string last, // float g) is calledStudent s3(“13579”, “Joe”, “Clifton”, 3.9);
// Student(string sID, float g) is calledStudent s(“12345”, 3.3);
// No default constructor if a constructor is defined.Student s4();
17
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)
*/
};
18
Class Constructors// InvalidStudent s1(“56789”);
// InvalidStudent s2(“Qi”, “Yang”);
// InvalidStudent s3(“13579”, “Joe”, “Clifton”, 3.9);
// InvalidStudent s(“12345”, 3.3);
// Default constructor is good!Student s4();
// Will not work!s4.Write();s4.UpdateGPA( 0.1 );
19
Copy Constructor
class Student
{
private:
string id, firstName, lastName;
float gpa;
public:
Student(string sID, string first, string last, float g)
// Copy constructor:
// gets initial values from object s
Student( Student s)
{
id = s.id;
firstName = s.firstName;
lastName = s.lastName;
gpa = s.gpa;
}
};20
Class Constructors
// Student(String sID, string first, string last, // float g) is calledStudent s1(“13579”, “Joe”, “Clifton”, 3.9);
int x, y = 10;
// Copy constructor is calledStudent s2(s1);
// Similar to the copy constructorx = y;
s2.Write();
s2.UpdateGPA( 0.1 );
s2.Write();21
Schedule
• Quiz7-2: Due Wednesday
• Program 5
Pairs by Wednesday
22
23
Test 1
Test 2
Test 3
FinalFinal
24
Good Luck!
• Come to classes/labs
• Do the work by yourself
• Get Help