# C++ Program to Find Area, Circumference of Circle

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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()
{
cout<<"Enter the Radius of Circle: ";
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()
{
cout<<"Enter the Radius of Circle: ";
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()
{
cout<<"Enter the Radius of Circle: ";
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()
{
cout<<"Enter the Radius of Circle: ";
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;
cout<<"Enter the Radius of Circle: ";
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):

```#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++ Online Test

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