Block 5: Classes
Carlos Díaz (cdv7@leicester.ac.uk)
Academic Year 2021-2022
EC7103-C++ Programming for Finance
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Introduction
Class: User-defined datatype which groups together related
pieces of information.
Example: We can define a class called student that will contain
the following information (fields or members).
ID number.
Mark in Coursework 1.
Mark in Coursework 2.
Mark in Coursework 3.
Mark in the Final Exam.
We can define this class as
class student {
public:
int IDnumber;
double CW1;
double CW2;
double CW3;
double FE;
};
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Objects
An instance is an occurrence of a class (object).
We can declare an instance as follows:
class student {
public:
int IDnumber;
double CW1;
double CW2;
double CW3;
double FE;
};
int main(){
student student1;
student student2;
return 0;
}
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Accessing members
We can access the members of a class by using the dot (.)
operator.
int main(){
student student1;
student student2;
student1.IDnumber = 134876209;
cout << "The ID number of student 1 is\n";
cout << student1.IDnumber << endl;
return 0;
}
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Passing members to function
We can pass (by value or reference) classes to functions
double mark(student s){
double mark = 0.0;
return mark = (s.CW1+s.CW2+s.CW3+s.FE)/4.0;
}
int main(){
student student1;
student1.IDnumber = 135675943;
student1.CW1 = 85.0;
student1.CW2 = 90.0;
student1.CW3 = 75.0;
student1.FE = 60.0;
double mark_student1 = mark(student1);
cout << "The mark of student with ID no "
<< student1.IDnumber << " is " << mark_student1;
return 0;
}
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Methods
Methods are functions which are part of a class.
mark is a method of the class student.
The following print function is also a method of the same class.
void print(student s)
{
cout << "Student ID number " << s.IDnumber << endl;
cout << "Mark in Coursework 1 " << s.CW1 << endl;
cout << "Mark in Coursework 2 " << s.CW2 << endl;
cout << "Mark in Coursework 3 " << s.CW3 << endl;
cout << "Mark in the final exam " << s.FE << endl;
}
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Implementing methods separately
We can create a header file with extension .h containing
members and methods and named after the class
#ifndef STUDENT_H_
#define STUDENT_H_
class student {
public:
int IDnumber;
double CW1;
double CW2;
double CW3;
double FE;
void print();
double mark();
};
#endif
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Implementing methods separately
Methods are usually programmed in a different cpp file.
#include
#include "student.h"
using namespace std;
double student::mark()
{
double mark = 0.0;
return mark = (CW1+CW2+CW3+FE)/4.0;
}
void student::print()
{
cout << "Student ID number " << IDnumber << endl;
cout << "Mark in Coursework 1 " << CW1 << endl;
cout << "Mark in Coursework 2 " << CW2 << endl;
cout << "Mark in Coursework 3 " << CW3 << endl;
cout << "Mark in the final exam " << FE << endl;
}
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Public and private members
Public members can be accessed from everywhere outside the
class (e.g. the main function).
Private members (default or declared under private:) can only
accessed within the class.
class student {
private:
int IDnumber;
double CW1;
public:
double CW2;
double CW3;
double FE;
};
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Constructors and destructors
A constructor is a member function invoked when an object is
declared.
Constructors initialize the members of the class.
A constructor must have the same name than the class.
If a constructor is not explicitly declared, the system will
automatically create one.
In our case, a constructor would be something like:
student(int id,double c1,double c2,double c3,double f)
{
IDnumber = id; CW1 = c1; CW2 = c2; CW3 = c3; FE = f;
}
We can use it when declaring an instance in the main function:
student student1(135675943,85.0,90.0,75.0,60.0);
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The vector class
The vector class allows to work with vectors.
To use the class we must include the header.
#include
A vector is declared as follows
vector name(size);
Some members of the vector class:
Member Function
size() Return the size
resize(a,b) Change the size
assign(a,b) Assign values to vector
push_back(a) Append an element at the end
clear Clear the content
insert(i,a) Inserts ’a’ in position ’i-1’
erase(i) Erase the element in position ’i’
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The vector class
Vectors are similar to arrays.
vector v1;
for(int i=1;i<=100;i++){
v1.push_back(i);
cout << v1[i-1] << endl;
}
double mean = 0.0;
for (int i=0;imean+=v1[i]/v1.size();
}
double var = 0.0;
for (int i=0;ivar+=(v1[i]-mean)*(v1[i]-mean)/(v1.size()-1);
}
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The vector class
Vectors can be passed as arguments of functions.
double mean_var(vector x, double& var)
{
double mx = 0.0;
for (int i=0;imx+=x[i]/x.size();
}
for (int i=0;ivar+=(pow((x[i]-mx),2))/(x.size()-1);
}
return mx;
}
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The vector class
We can use vectors to load data from an external file.
ifstream source("file.txt");
vector y;
double a;
if (source.is_open()){
while(!source.eof()){
source >> a;
y.push_back(a);
}
source.close();
}
We need to include vector and fstream.
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Seminar Question
Download the file data.txt
Load it to a new cpp file
Calculate and display the mean of this data
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