# 2.6. Studio: Area of a Circle¶

To get started, create a new console application in Visual Studio for the studio.

## 2.6.1. Calculate the Area of a Circle¶

Write a program that prompts the user for the radius of a circle. Calculate the area of the user’s circle and print the result.

Tip

Recall that the area of a circle is `A = pi * r * r`

where `pi`

is
3.14 and `r`

is the radius.

Here’s an example of how your program should work:

```
Enter a radius: 2.5
The area of a circle of radius 2.5 is: 19.625
```

Some questions to ask yourself:

- What data type should the radius be?
- What is the best way to get user input into a variable
`radius`

of that type?

Note

Use the `System.Math`

class in C# to get the value of pi and square the radius.
The documentation has guidance on how to use the `PI`

field and the `Pow`

method.

## 2.6.2. More Calculations¶

- Using the same radius, calculate the circumference (
`2*pi*r`

) and diameter of the circle (`2*r`

). - Output the results.

## 2.6.3. Road Trip!¶

- Ask the user for the miles per gallon of their car.
- If the radius that they entered is in miles, output how many gallons of gas they will use to go around this circle.

## 2.6.4. Bonus Missions¶

- Think about how we could make this program more modular by breaking out some of the code into a separate class. For example, we could pull out the circle information into a
`Circle`

class and leave the user questions and console messages in`Program`

. Take a look at the using statement for a refresher on how to reference another class file. - Extend your program further by using a while or do-while loop, so that when the user enters a negative number they are re-prompted for a radius.
- Add additional validation to your program. If the user enters a non-numeric character or a empty string? Print an error message and quit. You’ll need to peek ahead to learn about conditional syntax in C#.