In this article, you will learn and get code on finding the area and circumference of a circle based on its radius entered by user at run-time in C++ programming. Here are the list of approaches used:
Before starting the program, let's first get the formula used to find area and circumference of a circle.
To find area of a circle, use this formula:
area = 3πr2
The value of π is 3.14. And r indicates radius of circle. This formula can also be written as:
area = 3*3.14*r*r
To find circumference of a circle, use this formula:
circumference = 2πr
Now let's move on to the program.
To calculate area of any circle in C++ programming, you have to ask from user to enter the radius of circle, place the radius in a variable say rad and then initialize 3.14*rad*rad in a variable that holds the value of area of circle, as shown here in the following program.
// C++ Program to Find Area of a Circle
// ----codescracker.com----
#include<iostream>
using namespace std;
int main()
{
float rad, area;
cout<<"Enter the Radius of Circle: ";
cin>>rad;
area = 3.14*rad*rad;
cout<<"\nArea of Circle = "<<area;
cout<<endl;
return 0;
}
This program was build and run under Code::Blocks IDE. Here is its sample run:
Now enter the radius of circle say 5 and press ENTER key to see the following output:
You can also replace the variable rad with r to make above program more meaningful.
Let's create the same purpose program using a user-defined function findArea(). This function takes radius as its argument and returns the area of circle. The question is, write a program in C++ to find the area of a circle using user-defined function. Answer to this question is given below:
// Area of Circle using Function
// ----codescracker.com----
#include<iostream>
using namespace std;
float findArea(float);
int main()
{
float rad, area;
cout<<"Enter the Radius of Circle: ";
cin>>rad;
area = findArea(rad);
cout<<"\nArea of Circle = "<<area;
cout<<endl;
return 0;
}
float findArea(float r)
{
return (3.14*r*r);
}
It will produce the same output as of previous one.
The question is, write a program in C++ to find circumference of a circle. The answer to this question is:
// C++ Program to Find Circumference of a Circle
// ----codescracker.com----
#include<iostream>
using namespace std;
int main()
{
float rad, circum;
cout<<"Enter the Radius of Circle: ";
cin>>rad;
circum = 2*3.14*rad;
cout<<"\nCircumference of Circle = "<<circum;
cout<<endl;
return 0;
}
Here is the initial snapshot of the sample run:
Now enter the radius of circle to see its circumference. Here is the final snapshot of sample run, supposing that user enters 5 as radius of circle:
This program does the same job as of previous program, but using a function named findCircum()
// Circumference of Circle using Function
// ----codescracker.com----
#include<iostream>
using namespace std;
float findCircum(float);
int main()
{
float rad;
cout<<"Enter the Radius of Circle: ";
cin>>rad;
cout<<"\nCircumference of Circle = "<<findCircum(rad);
cout<<endl;
return 0;
}
float findCircum(float r)
{
return (2*3.14*r);
}
This program produces the same output as of previous one.
This is the last program of this article. This program finds both area and circumference of a circle using an object oriented feature of C++, that is class.
// Area and Circumference of Circle using Class
// ----codescracker.com----
#include<iostream>
using namespace std;
class CodesCracker
{
public:
float findArea(float r)
{
return (3.14*r*r);
}
float findCircum(float r)
{
return (2*3.14*r);
}
};
int main()
{
CodesCracker c;
float rad, area, circum;
cout<<"Enter the Radius of Circle: ";
cin>>rad;
area = c.findArea(rad);
circum = c.findCircum(rad);
cout<<"\nArea of Circle = "<<area;
cout<<"\nCircumference of Circle = "<<circum;
cout<<endl;
return 0;
}
Here is the sample run of above program with user input as 5 (radius of circle):
To learn more about class, you can follow the separate tutorial on it. Above program can also be written as:
// ----codescracker.com----
#include<iostream>
using namespace std;
class CodesCracker
{
private:
float r;
public:
void getData();
float findArea();
float findCircum();
};
void CodesCracker::getData()
{
cout<<"Enter the Radius of Circle: ";
cin>>r;
}
float CodesCracker::findArea()
{
return (3.14*r*r);
}
float CodesCracker::findCircum()
{
return (2*3.14*r);
}
int main()
{
CodesCracker c;
c.getData();
cout<<"\nArea of Circle = "<<c.findArea();
cout<<"\nCircumference of Circle = "<<c.findCircum();
cout<<endl;
return 0;
}