This unit has the following objectives
· To understand the importance of object oriented programming approach over procedural languages
· To learn the basic features supported by OOP languages
· To learn the basic construct of a C++ program and learn to compile and execute it
1.2 Evolution of Programming methodologies
The programming languages have evolved from machine languages, assembly languages to high level languages to the current age of programming tools. While machine level language and assembly language was difficult to learn for a layman, high level languages like C, Basic, Fortran and the like was easy to learn with more English like keywords. These languages were also known as procedural languages as each and every statement in the program had to be specified to instruct the computer to do a specific job. The procedural languages focused on organizing program statements into procedures or functions. Larger programs were either broken into functions or modules which had defined purpose and interface to other functions.
Procedural approach for programming had several problems as the size of the softwares grew larger and larger. One of the main problems was data being completely forgotten. The emphasis was on the action and the data was only used in the entire process. Data in the program was created by variables and if more than one functions had to access data, global variables were used. The concept of global variables itself is a problem as it may be accidentally modified by an undesired function. This also leads to difficulty in debugging and modifying the program when several functions access a particular data.
The object oriented approach overcomes this problem by modeling data and functions together there by allowing only certain functions to access the required data.
The procedural languages had limitations of extensibility as there was limited support for creating user defined datatypes and defining how these datatypes will be handled. For example if the programmer had to define his own version of string and define how this new datatype will be manipulated, it would be difficult. The object oriented programming provides this flexibility through the concept of class.
Another limitation of the procedural languages is that the program model is not closer to real world objects . For example, if you want to develop a gaming application of car race, what data would you use and what functions you would require is difficult questions to answer in a procedural approach. The object oriented approach solves this further by conceptualizing the problem as group of objects which have their own specific data and functionality. In the car game example, we would create several objects such as player, car, traffic signal and so on.
Some of the languages that use object oriented programming approach are C++, Java, Csharp, Smalltalk etc. We will be learning C++ in this text to understand object oriented programming. C++ is a superset of C. Several features are similar in C and C++.
Self Assessment Questions
1. List the limitations of procedural languages
2. _______ is an OOP Language
3. In OOP approach programmers can create their own data types. True/False
4. In procedural languages, the programs are written by dividing the programs into smaller units known as __________
1.3 Introduction to OOP and its basic features
As discussed earlier, one of the basic concept in Object Oriented Programming approach is bundling both data and functions into one unit known as object. The functions of a particular object can only access the data in the object providing high level of security for the data. The functions in the object are known as member functions or sometimes as methods.
The key features of OOP programming languages are:
· Objects and Classes
An Object is a program representation of some real-world thing (i.e person, place or an event). Objects can have both attributes(data) and behaviours (functions or methods). Attributes describe the object with respect to certain parameters and Behaviour or functions describe the functionality of the object.
Table 1.1 Example of Objects
According to Pressman, Objects can be any one of the following:
a) External entities
b) Things
c) Occurrences or events
d) Roles
e) Organisational units
f) Places
g) Data Structures
For example, objects can be an menu or button in an graphic user interface program or it may be an employee in an payroll application. Objects can also represent a data structure such as a stack or a linked list. It may be a server or a client in an networking environment.
Objects with the same data structure and behavior are grouped together as class. In other words, Objects are “instances” of a class. Classes are templates that provide definition to the objects of similar type. Objects are like variables created whenever necessary in the program. For example, Employee may be a class and Pawan, Sujay and Ganesh are objects of the class employees. Just as you can create as many variables of a default datatype such as integer, you can create as many objects of a class.
Classes and Objects support data encapsulation and data hiding which are key terms describing object oriented programming languages. Data and functions are said to be encapsulated in an single entity as object. The data is said to be hidden thus not allowing accidental modification.
· Inheritance
Inheritance is one of the most powerful feature of Object Oriented Programming Languages that allows you to derive a class from an existing class and inherit all the characteristics and behaviour of the parent class. This feature allows easy modification of existing code and also reuse code. The ability to reuse components of a program is an important feature for any programming language
· Polymorphism and Overloading
Operator overloading feature allows users to define how basic operators work with objects. The operator + will be adding two numbers when used with integer variables. However when used with user defined string class, + operator may concatenate two strings. Similarly same functions with same function name can perform different actions depending upon which object calls the function. This feature of C++ where same operators or functions behave differently depending upon what they are operating on is called as polymorphism (Same thing with different forms). Operator overloading is a kind of polymorphism.
OOP approach offers several advantages to the programmers such as
· Code can be reused in situations requiring customization
· Program modeling and development closer to real world situations and objects
· Easy to modify code
· Only required data binded to operations thus hiding data from unrelated functions
Self Assessment Questions
1. _____________ feature in OOP allows to reuse code.
2. The concept of bundling data and functions into single unit is termed as ___________
3. Object is an __________ of a class
4. Give an example of a class and an object
5. ______________ is an advantage of OOP approach
1.4 Basic components of a C++ Program and program structure
The C++ is a superset of C. At the basic level, the programs look similar in both C and C++. Every statement in C++ ends with a semicolon (;). All the reserved words have to be written in small case and the c++ compiler is case sensitive. Data in programming languages are stored in variables. To create a variable, the variable should support an inbuilt datatype. The variable is a name given to a particular location in the memory and the value stored in a variable can be altered during program execution. The datatypes supported in C++ are listed below
Table 1.2 Basic Datatypes in c++
| Data Type | Size (in bytes) | Values that can be taken |
| Int | 2 | -32768 to 32767 |
| Bool | 1 | False and true / 0 and 1 |
| Char | 1 | -128 to 127 |
| Long | 4 | -2,147,483,648 to 2,147,483,647 |
| Float | 4 | 3.4 X 10-38 to 3.4 X 1038 (Precision 7) |
| Double | 8 | 1.7 X 10-308 to 1.7 X 10308 (Precision 15) |
| Long double | 10 | 3.4 X 10-4932 to 1.1 X 104932 (Precision 19) |
| Unsigned int | 2 | 0 to 65,535 |
· Can comprise of 1 to 8 alphabets, digits or underscore
· First character should be an alphabet
· Names are case sensitive
· Reserve words of c++ cannot be used
Variables have to be declared before using them in the program. The declaration is done in the following way:
datatype variablename
Eg: int data ;
The above declaration declares a integer variable named data. The value stored in int data by default is a junk value. Values can also be assigned to the variable during declarations or initialized separately using the assignment operator =.
Eg: int data=0;
Or
int data;
data=0;
Constants are those which do not change during execution of a program. The constants in C++ can be numeric, character or string constants. Examples of each are shown in table 1.3
Table 1.3 Example of Constants
Constant | Example | Constraints |
| Numeric Constant | 23000 450.6 (Floating point) | Can be negative or positive, cannot contain blanks or commas, or $ |
| Character Constant | ‘A’ | Any character enclosed within single quotes, represented by unique ASCII number in the memory |
| String Constant | “Hello” | Set of characters enclosed in double quotes, last character in the string is null character ‘\0’ |
Table 1.4 Operators in C++
| Arithmetic Operators | Type | Action |
| - | Unary as well as binary | Subtraction for binary and minus for unary |
| + | Binary | Addition |
| * | Binary | Multiplication |
| / | Binary | Division |
| % | Binary | Modulus (remainder after dividing) |
| -- | Unary | Decrement value by one |
| ++ | Unary | Increment value by one |
| Relational Operators | Type | Action |
| > | Binary | Greater than |
| >= | Binary | Greater than or equal |
| < | Binary | Less than |
| <= | Binary | Less than equal |
| == | Binary | Comparision for equality |
| != | Binary | Comparision for inequality |
| Logical Operators | Type | Action |
| && | Binary | AND |
| || | Binary | OR |
| ! | Unary | NOT |
// sum.cpp
#include<iostream.h>
void main()
{
int a,b,sum;
cout<<”Please enter any two numbers”<<endl;
cin>>a>>b;
sum=a+b;
cout<<”Sum of two numbers is ”<<sum;
}
The above program asks the user to enter two numbers and displays the sum of the two numbers. Iostream.h is a header file. The first statement of the above program is required if you would like to include the cin and cout statements which is used for standard input or input from keyboard and standard output or output to display screen. cin and cout are actually predefined objects in C++. Iostream.h file contains the declarations for using the cin and cout statements. There are several such header files which have to be included depending on the functions you are using. We will come across many such header files as we progress.
Every C++ program should have a main() function. C++ allows you to create your own functions in the program, like C. However the program execution always begins with the master function main(). Paranthesis are used to group statements belonging to one function or program statement. Every opening parathesis ({ ) should have a matching closing parathesis ( }).
The third statement declares three integer variables a, b and sum. The fourth statement displays “Please enter any two numbers” on the display screen using cout statement. Cout (pronounced as C out) uses << or insertion operator to push data to the output stream.
Operators known as manipulators can be used along with the << operator to modify the way data is displayed. Endl is an operator which is similar to ‘\n’ character in C that inserts a linefeed into the output. The first cout statement in the program displays a statement where as the second cout statement displays a statement and the value stored in the variable sum.
Cin (pronounced as c in) statement uses >> or extraction operator to feed the data to the input stream. The above cin statement waits for user to enter two integers. The values entered by the user is then stored in the variables a and b. Each variable in cin statement should separated by >> operator.
Comment statements can be included in the program by prefixing the statement with “//” for single line comments. Comments add clarity to the program. Multiple line comments can be added by enclosing the statements between /* and */.
Self Assessment Questions
1. ______________ is a header file used in c++ that handles input and output functions.
2. ____________ statement is used to input data from the user in c++.
3. ______________ statement is used to display data on the display screen in c++.
4. ______________ is a master function required in all C++ program and program execution begins from the first statement of this function.
1.5 Compiling and Executing C++ Program
1. There are three steps in executing a c++ program: Compiling, Linking and Running the program. The c++ programs have to be typed in a compiler. All the programs discussed in the book will be compiled on turbo c++ compiler. The turbo c++ compiler comes with an editor to type and edit c++ program. After typing the program the file is saved with an extension .cpp. This is known as source code. The source code has to be converted to an object code which is understandable by the machine. This process is known as compiling the program. You can compile your program by selecting compile from compile menu or press Alt+f9. After compiling a file with the same name as source code file but with extension .obj. is created.
Second step is linking the program which creates an executable file .exe (filename same as source code) after linking the object code and the library files (cs.lib) required for the program. In a simple program, linking process may involve one object file and one library file. However in a project, there may be several smaller programs. The object codes of these programs and the library files are linked to create a single executable file. Third and the last step is running the executable file where the statements in the program will be executed one by one.
Fig 1.1 shows the entire process. When you execute the program, the compiler displays the output of the program and comes back to the program editor. To view the output and wait for user to press any key to return to the editor, type getch() as the last statement in the program. Getch() is an inbuilt predefined library function which inputs a character from the user through standard input. However you should include another header file named conio.h to use this function. Conio.h contains the necessary declarations for using this function. The include statement will be similar to iostream.h.
Fig. 1.1: Compiling and Linking
During compilation, if there are any errors that will be listing by the compiler. The errors may be any one of the following
1. Syntax error
This error occurs due to mistake in writing the syntax of a c++ statement or wrong use of reserved words, improper variable names, using variables without declaration etc. Examples are : missing semi colon or paranthesis, type integer for int datatype etc. Appropriate error message and the statement number will be displayed. You can see the statement and make correction to the program file, save and recompile it.
2. Logical error
This error occurs due to the flaw in the logic. This will not be identified by the compiler. However it can be traced using the debug tool in the editor. First identify the variable which you suspect creating the error and add them to watch list by selecting Debug ->Watches->Add watch. Write the variable name in the watch expression. After adding all the variables required to the watch list, go to the statement from where you want to observe. If you are not sure, you can go to the first statement of the program. Then select Debug ->Toggle Breakpoint (or press ctrl + f8). A red line will appear on the statement. Then Run the program by selecting Ctrl + f9 or Run option from run menu. The execution will halt at the statement where you had added the breakpoint. The watch variables and their values at that point of time will be displayed in the bottom in the watch window. Press F8 to execute the next statement till you reach the end of the program. In this way you can watch closely the values in the watch variables after execution of each and every statement in the program. If you want to exit before execution of the last statement press Ctrl + Break. To remove the breakpoint in the program go to the statement where you have added breakpoint select Debug ->Toggle Breakpoint (or press ctrl + f8). Select Debug -> watch ->remove watches to remove the variables in the watch list. This tool helps in knowing the values taken by the variable at each and every step. You can compare the expected value with the actual value to identify the error.
3. Linker error
This error occur when the files during linking are missing or mispelt
4. Runtime error
This error occurs if the programs encounters division by zero, accessing a null pointer etc during execution of the program
Self Assessment Questions
1. ___________, ______________ and _____________ are phases in execution of a C++ program
2. The logical error is identified by the compiler. True/False
3. ________________ is the extension of C++ program source files
4. ________________ is the extension of C++ object code
Summary
Object oriented Programming enables storing data and functions together which enables hiding data from unnecessary exposure. Procedural languages differs from the Object oriented programming in the approach used in solving the problem. While the former focuses on organizing programs around functions, the later focuses organizing programs around classes. Classes allow users to define their own datatypes and functionality. This allows extension of the basic datatypes supported by the language. Reusability of code through inheritance allows users to use the existing code without modifying it but also extend the functionality of the existing code. The C++ programs are similar to C except for the object oriented programming features. Every C++ program has a main function from where the execution starts. C++ programs goes through two phases ie compiling and linking before execution.
Terminal Questions
1. Which of the following is not a feature of Object Oriented Programming
a. Data encapsulation b. Inheritance c. Operator Overloading
d. Data Structure
2. Which one of the following is not an inbuilt basic datatype in c++
a. Int b. Bool c. String d.Float
3. Write a program that accepts two numbers from the user and swaps the two numbers without using a temporary variable.
4. Write a program that accepts two numbers a and b and divides a by b and displays the quotient and the remainder.
5. Object constitutes of ____________ and _____________
Answers to SAQs and TQs
Answers to SAQs in 1.2
1. Limitations of procedural languages are no importance to data and inability to define user defined datatypes and define functionality for the same
2. C++, smalltalk, Java are all OOP Languages
3. True
4. Functions or procedures
Answers to SAQs in 1.3
1. Inheritance
3. Data Abstraction
4. Object is an instance of a class
5. Class - car and object – Maruti 800
6. Reusability of code
Answers to SAQs in 1.4
1. iostream.h
2. cin
3. cout
4. main() function
Answers to SAQs in 1.5
1. Compiling, Linking and Running
2. False, it can assist in identifying using debug tool
3. .cpp
4. .obj
Answers TQs
1. d
2. c
3. Program to swap two numbers without using a temporary variable
# include<iostream.h>
void main()
{ int num1,num2;
cout <<” enter two numbers”;
cin>> num1>>num2;
Num1=num1+num2;
Num2=num1-num2;
Num1=num1-num2;
cout<< “numbers after swapping are ”<<num1<<num2;
}
4. Program to divide a and b and display quotient and remainder
# include<iostream.h>
void main()
{ int a,b, q, rem;
cout <<” enter two numbers”;
cin>> a>>b;
q=a/b;
r=a%b;
cout<< “Quotient = ”<<q<<endl;
cout<<”remainder=”<<r;
}
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