C++ Refresher - Part One

This article is about the ways in which C# and C++ are similar and where these languages differ. You are familiar with the concepts of OOP language. You may have already studied one such language, called C#. If not, then there is no problem.

In this session, you will learn about:

• Variables and data types
• Storing data in a variable and displaying data on the screen
• Creating and executing a C++ program
• Classes in C++
• Member functions

Before we start the session, let us revisit the features of Object-Oriented Programming (OOP) language.



In order to perform a specific task on a computer, you need to write a set of instructions known as a program. While creating a program, you may need to temporarily store some values by using variables.

Variables and Data Types

The syntax to declare a variable is:

• <data type><variable name>;

Examples:

• int num1;
• char chr;

Data types can be categorized into the following types:



The following table lists the common built-in data types used in C++ and C#.

Data Type	Number of Bytes in C++	Number of Bytes in C#
char	1	2
int	2 or 4	4
float	4	4
double	8	8

The data type equivalent to string in C++ is a character array.

The following table shows the use of a string variable and a character array.

C#	C++
string str = “India”;	char str[] = “India”;

 




Let us see how these objects are used in C++

In C++, we use predefined objects to store and display data.



Storing Data in a Variable and Displaying Data on the screen

#include<iostream.h>
int num1, num2, sum;
cout<<“Enter number 1”<<endl;
cin>>num1;
cout<<“Enter number 2”<<endl;
cin>>num2;
sum = num1 + num2;
cout<<“The sum is:”<<sum;

Once you have created a C++ program, you need to compile and execute it. Let us now compile and execute a C++ program,

• Similar to C#, a C++ program must contain the main() function. 
• C++ is not a pure object-oriented language like C#. 
• Therefore, you can create a program in C++ without using a class as in the following code:
  

  #include < iostream.h >
      void main()
      {
          int num1, num2, sum;
          cout << “Enter number1” << endl;
          cin >> num1;
          cout << “Enter number2” << endl;
          cin >> num2;
          sum = num1 + num2;
          cout << “The sum is: ” << sum;
      }

Classes in C++

Object-oriented programming languages, such as C# and C++, use classes to group objects having common attributes.

• A class is declared by using the class keyword.
• The syntax of a class in C++ is:

class<class_name>
{
...
};

In C#, a program cannot be created without a class. However, in C++ you can create a program with/without a class.

A class consists of:

• Attributes: Represented using member variables
• Behaviors: Represented using member functions

Member Functions



A function consists of the following parts:

• Declaration: Syntax for declaring a function:

<return type><function name><function parameters>;

• Definition: Syntax for defining a function:

<return type><function name><function parameters>
{
... }



The following table shows the use of member functions in C# and C++.

C# (function declared and defined inside the class body)	C++ (function declared and defined inside the class body)	C++ (function declared inside and defined outside the class body)
class Sum { public void Add() { //Function Body } }	class Sum { void Add() { //Function Body } };	class Sum { void Add(); //Declaration }; void Sum::Add() //Definition { //Function Body }

Now, let us see how the same function can be modified to accept the numbers as arguments. Consider the following code snippet in which the Add() function accepts two numbers from a user and adds them:

class Sum
{
    void Add(); //Declare the member function
};
void Sum::Add() //Defining the member function
    {
        int num1, num2, sum;
        cout << “Enter number 1” << endl;
        cin >> num1;
        cout << “Enter number 2” << endl;
        cin >> num2;
        sum = num1 + num2;
        cout << “The sum is: ” << sum;
    }

Types of Function Arguments

A function can have the following types of arguments:

• Default arguments
• Constant arguments

The following table shows the use of default and constant arguments.

Default arguments	Constant arguments
void Add(int iNum1=10, int iNum2=20) { //Function Body }	void Add(constint iVar1, constint iVar2) { //Function Body }