C++ Comments

The program that you write should be clear not only to you, but also to the reader of your program. Part of good programming is the inclusion of comments in the program. Typically, comments can be used to identify the authors of the program, give the date when the program is written or modified, give a brief explanation of the program, and explain the meaning of key statements in a program.

Comments are for the reader, not for the compiler. So when a compiler compiles a program to check for the syntax errors,it completely ignores comments.

Single Line Commenting

// is used to comment on one line.

Single-line comments begin with // and can be placed anywhere in the line. Everything encountered in that line after // is ignored by the compiler.

Examples

//  My first comment

// Variable for firstname

char first_name;

//prints: 7 + 8 = 15

cout << "7 + 8 = " << 7 + 8<< endl;

You can put comments at the end of this line as follows:

cout << "7 + 8 = " << 7 + 8<< endl; //prints: 7 + 8 = 15

Block Commenting

Block comment begins with /* and ends with */

Thus:

/* comment line 1

    Comment line2

    Comment line3

    …

*/

Examples:

/*

   Last updated 07/06/2019

   An application to register students

   Variables And What they stand for

    first_name  : for first name ofthe student

    surname : for the surname of the student

    age: for the age of the student

*/

Inputand Output statement

The variable cin has access to operators and functions that can be used to extract data from the standard input device.

Input Statement

Data can be extracted from the standard input device by using the cin and the extract operation.

The syntax of an input statement using cin and the extraction operator >> is:

cin >>variable;

e.g

inta,b,c;

cin>> a;

a = value entered

cin>>b;

b = value entered

cin>>c;

c = value entered;

Youcan extract the multiple data at once using just a single cin in the format below.

cin >> variable>> variable...;

Thus:

cin >> a>> b >> c;

Output Statement

The syntax for output of  is:

cout<< expression or manipulator << expression or manipulator...;

Examples

cout<< “My name is Godwin Ashong”;

cout<< “I am a Ghanaian”;

In order to print out on a new line, the syntax endl is added to the syntax prior to the syntax that prints the text on a new line;

The above syntax prints out “My name is Godwin Ashong I am a Ghanaian”

In order to print out:

My name is Godwin Ashong

I am a Ghanaian

The syntax << endl needs to be added to the cout <<”My name is Godwin Ashong”

Thus the new syntax will be:

cout<< “My name is Godwin Ashong” <

cout<< “I am a Ghanaian”;

Operators

An operator is a symbol that tells the compiler to perform specific mathematical or logical manipulations.

Arithmetic Operators

There are following arithmetic operators supported by C++ language −

Assume variable A holds 10 and variable B holds 20, then −

Examples

Constant

The keyword const means that a variable cannot be changed once it has been declared and

initialized.

The syntax below is used to declare a constant.

const variable type variable name = value;

Thus you type const then the variable type and leave a space and then variable name then assign the value of the constant.

Examples

const double PI = 3.1415926535;

const double acceleration = 9.8;

APPLICATION OF CONCEPTS

1.      Write an application in C++ that calculates the area of a circle when a user enters the radius

2.      Write an application in C++ that calculates the force on a body when the mass is entered.

SOLUTION CODES

1.      APPLICATION TO CALCULATE THE AREA OF A CIRCLE

#include <iostream>

using namespace std;

/*
    An application to calculate the area of a circle
    Formula of area of a circle = pi x radius x radius
*/
int main()
{
    const double PI = 3.1415926535;
    float radius,area;
    //Alert user to enter the radius
    cout << "Please enter the radius of the circle"<<endl;
    //Get the radius of the circle from the user
    cin >> radius;
    //Calculate the area of the circle
    area = PI*radius*radius;
    // Display the value of the area to the user
    cout << "The area of the circle of radius "<<radius<<" is "<<area<<endl;
    return 0;
}

2.     APPLICATION TO CALCULATE THE FORCE OF A BODY

#include <iostream>

using namespace std;

/*
    An application to calculate the force of a body
    Formula of calculating the force of a body = mass x acceleration due to gravity
*/
int main()
{
    const double acceleration_due_to_gravity = 9.8;
    float mass,force;
    //Alert user to enter the mass
    cout << "Please enter the mass of the body"<<endl;
    //Get the mass from the user
    cin >> mass;
    //Calculate the force
    force = mass*acceleration_due_to_gravity;
    // Display the value of the area to the user
    cout << "The force of the body of mass "<<mass<<"kg is "<<force<<"N"<<endl;
    return 0;
}

ASSIGNMENT 2

Write an application in C++ that takes the temperature in degree Celsius and concerts it to Fahrenheit.