# Calculate area of a circle in C++

###### cin - Question 13

In this question, we will see how to input the radius of a circle in C++ programming using the cin statement and find its area. To know more about cin statement click on the cin statement lesson.

**Q13)** Write a program in C++ to input the radius of a circle and find its area. Area of a circle is πr^{2}. Where r is the radius and the value of π (pie) is 22/7 or 3.142

Formula: area = 3.142 * r * r

#### Program

```
#include <iostream>
#include <conio.h>
using namespace std;
int main()
{
float r,a;
cout<<"Enter radius of a circle ";
cin>>r;
a=3.142*r*r;
cout<<"Area="<<a;
return 0;
}
```

#### Output

Enter radius of a circle 5 Area=78.55