C++ Notes

1. Brief Summary of C++ (Mainly on Class)
Attributes of OOP
1) Encapsulation
a. Hide the data (make the data variable private) and hide the internal
function that is not needed by the external user
b. Only exposes the functions that are required by the external user. User
calls these public functions in order to use the object.
2) Code reuse
a. Use inheritance to reuse existing code
3) Abstraction
Use class to model the things you have in your program. Program consist of
objects that talk to each other by calling each other public member function.
4) Generalization
a. Use template class or template function to build generic class or function
b. Generic function can process different type of data
c. Build a general class and use it as a base to derive specialized class
(inheritance)
Variable
- Refers to memory location used to store data
- Is given a name example weight, myID . It is not convenient to memorize memory
address e.g A1230000FFA
Variable data type can be classified to a few types
a) Simple data type
int, char , float, double
int weight = 0; // declare and initialize the variable in 1 line
of code.
b) Array
Array is a compound data type whereby it stores a group of data
int weightArray[5] ; // declare an array called weightArray to
store 5 integer type data
int weightArray[5] ; // declare an array called weightArray to
store up to 5 integer type data
int weightArray2[5] = {1,2,3,4,5}; // You can also declare and
initialize
cout << endl << weightArray2[2] ; //% display the 3rd element
c) Pointer
Pointer is a type of variable that is used to represent other variable
It is mainly used to represent an array, object and also to pass data to a function
by reference. In addition the function can pass data to the pointer so that it can be
retrieved by the caller function.
Pointer stores the address of the variable that it points to.
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2. int* ptr ; // declare a pointer to int and name the pointer as
ptr
int* ptr2 = &weight ; // declare a pointer to int and initialize
it to point to the variable weight in 1 line of code
ptr = &weight2 ; // The previously declared pointer is now
pointed at the variable weight2
cout << endl << *ptr2 << endl ; // display the data in the
variable pointed by ptr2, display 0 since weight=0
Using pointer to represent array
int* arrayPtr;
arrayPtr = weightArray2 ; //arrayPtr now points to the array
// weightArray2
// take note that the array name hold
the address of the array
cout << endl << arrayPtr ; // display the address of the 1st
element
cout << endl << arrayPtr+1 ; // display the address of the 2nd
element
cout << endl << *(arrayPtr) ; // display 1
cout << endl << *(arrayPtr+1) ; // display 2
cout << endl << arrayPtr[0] ; // display 1
cout << endl << arrayPtr[1] ; // display 2
char* mystring = "Hello" ;
cout << mystring;
const int* pt = weightArray ; // pt is a pointer to a constant,
you cannot use pt to change the value of weightArray
// *(pt+1) = 200 ; this is wrong
int* const pt2 = weightArray; // pt2 is a constant pointer, you
cannot use pt2 to point to other variable, pt2 always represents
weightArray // pt2 = weightArray2 , this is wrong
d) Reference
Reference is a variable that represent other variable as an alias.
It is mainly used to pass data to a function by reference. In addition the function
can pass data to the reference variable so that it can be retrieved by the caller
function.
int& rnum = weight2; // declare a reference variable by the name
rnum and initialize it to represent weight2
// reference variable must always
be initialized when it is first declared
cout << endl << rnum ; // display 10, the value of weight2
rnum = weight ; // reassign rnum to represent the variable
weight
cout << endl << rnum ; // display 0, the value of weight
e) Class and Structure
In C++ there are many predefined variable type such as int, char, float
However you can also create your own data type using the class and struct
construct.
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3. Class is a c++ language construct that is used as a blueprint to create objects
Object is an instance of the class and is a variable.
Object contain member function and member variable. Member function provide
the service and member variable store data.
Member can be private , public, protected
// Declare a class by the name of Student
// the purpose or responsibility of Student class is to store
students information
// To fulfill its responsibility , it provides a set of services
to the user
// User can invoke the public member function for example
getCgpa() to retrieve the cgpa value stored in the object
class Student {
public:
Student(); // default constructor
Student(float p_cgpa) { _cgpa = p_cgpa ;} // parameterized
constructor
Student(string name);
Student(string name, string address);
float getCgpa(); // member function
void set_CgpaAndAge( float p_cgpa, int p_age) {
_cgpa = p_cgpa ;
_age = p_age;
}
void setName(string pName) { _name = pName;}
string getAddress();
void getcgpaAndAge(float& p_cgpa, int& p_age);
private:
string _name;
string _address;
char _icNumber[20];
float _cgpa;
int _age;
} ;
// Test program to test the class and its member function defined above
int main()
{
Student stud1("Lim"); // Create the object called stud1 and
initialize its name
stud1.set_CgpaAndAge(3.99,20); // set the cgpa value and age of
object stud1
}
Getting function to return more than one value
Suppose in the main function we want to retrieve the cgpa and age value of the
object, we cannot write a function to return 2 values. A function can only return 1
value. One way to solve this problem so that a function can pass more than 1
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4. variable back to the caller function is to use the reference variable as the function
argument.
main( )
{ int x=0, y=0;
functionName(x,y) ;
cout << x << y ; // Display 100 200
}
void functionName (int& arg1, int& arg2)
{
arg1 = 100;
arg2 = 200;
}
This way the function functionName can return the 2 integer values 100, 200 back
to the main function. By using reference variable you can pass multiple data to a
function and also use it as container to store the data that need to be returned by
the function.
Here is the implementation for the Student class member function The main ()
function need to retrieve the cgpa value and the age value from the Student object
stud1.
1) Method 1 : Use a reference variable
// the function below retrieve the data _cgpa and _age from
the Student object and pass them to the reference variable
so that the caller function can get hold of this data
void Student::getcgpaAndAge(float& p_cgpa, int& p_age) {
p_cgpa = _cgpa ;
p_age = _age ; // assign member variable to argument
// variable
}
int main()
{
int age; float cgpa;
Student stud1("Lim"); // Create the object called stud1 and
initialize its name
stud1.set_CgpaAndAge(3.99,20); // set the cgpa value and
age of object stud1
stud1.getcgpaAndAge(cgpa, age); // request the stud1
object to get and return its cgpa value and age value
cout << endl << "cgpa = " << cgpa; // display 3.99
cout << endl << " age = " << age;
}
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5. Program output
Output of object s4
Ali
Output of object s4 access using pointer
Ali
Output of object s4 access using reference
Ali
Output of object ecpStudents[1]
ecpStudents[1]._name = Ah Kow
Output of object ecpStudents[2] in the array , this time the array is represented using the
pointer pStd
ecpStudents[2]._name = pStd[2]._name = Aminah
Use pointer pStd2 to represent the array of 3 Student objects, access the 2nd object
pStd2[1]._name = No name yet
This program allow the Student object to be added to the Subject object
Subject object has many Student object
Constructor called: Subject Name: ECP4206 OOP Programming
Number of Student are 2
Phua CK
Obama
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