## Area of Circle

To find the area of a circle whose radius is given, use `math.pi`

constant and apply the following formula.

`Area of Circle = math.pi * radius * radius`

## Program

In the following program, we shall define a function `areaOfCircle()`

that takes radius as an argument and return the area of circle.

We read radius as integer from user, call `areaOfCircle()`

with the radius passed as argument. You can also read radius as float from user using float() function. In the following program we use int() and you may try float() as practice.

**Input**

`radius`

of circle, where `radius>0`

.

**Python Program**

```
import math
def areaOfCircle(radius) :
if radius < 0:
print('Radius cannot be negative.')
return
return math.pi * radius * radius
r = int(input('Enter radius : '))
area = areaOfCircle(r)
print(f'Area of Circle : {area}')
```

**Output**

```
Enter radius : 5
Area of Circle : 78.53981633974483
```

**Important Points regarding above program**

- We imported Python math library to use the value of PI.
- input() function reads a string from standard input. Therefore, we have used int() function to convert string to integer.
- If given radius is less than zero, we are returning nothing.