C++ Program to Find Area, Circumference of Circle

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:

• Area of Circle without using Function
• Area of Circle using Function
• Circumference of Circle without using Function
• Circumference of Circle using Function
• Area and Circumference of Circle using Class

Before starting the program, let's first get the formula used to find area and circumference of a circle.

Area of Circle Formula

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

Circumference of Circle Formula

To find circumference of a circle, use this formula:

circumference = 2πr

Now let's move on to the program.

Find Area of Circle

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.

#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.

Using Function

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:

#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.

Find Circumference of Circle

The question is, write a program in C++ to find circumference of a circle. The answer to this question is:

#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:

Using Function

This program does the same job as of previous program, but using a function named findCircum()

#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.

Find Area and Circumference using Class

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.

#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:

#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;
}

Same Program in Other Languages

• C Find Area & Circumference
• Java Find Area & Circumference
• Python Find Area & Circumference
• Python Find Circumference

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