## C# program to find the circumference of a circle:

In this post, we will learn how to find the *circumference* of a *circle* in *C#*. If the radius of a *circle* is *r* and if *π* is the mathematical constant *PI*, we can find the *circumference* of a circle by using the below formula:

`Circumference = 2 * π * radius`

*π* is a mathematical constant and it’s value is already defined. So, if we can get the value of *radius* from the user, we can calculate the value of *circumference* or *perimeter* for that circle.

### C# program:

Let’s write down the program.

```
using System;
public class Program
{
public static void Main()
{
double radius;
double circumference;
Console.WriteLine("Enter the value of radius:");
radius = double.Parse(Console.ReadLine());
circumference = 2 * Math.PI * radius;
Console.WriteLine("Circumference :"+Math.Round(circumference, 2));
}
}
```

Here,

*radius*variable is to store the radius of the circle. It is reading the radius value from the user and storing it in the variable*radius*.- We are calculating the
*circumference*by using the above formula. The value of*π*is reading as*Math.PI*, which is the constant defined in the*Math*class. - The calculated
*circumference*is stored in the variable*circumference*. - The last line is printing the value of
*circumference*.

If you run this program, it will print output as like below:

```
Enter the value of radius:
13
Circumference :81.68
```

### Calculate the circumference by using a separate function:

We can also use a *separate function* to calculate the *circumference*. This function will take the *radius* of the circle as parameter and return the *circumference* of that circle.

Below is the complete program:

```
using System;
public class Program
{
public static double getCircumference(double radius){
return 2 * Math.PI * radius;
}
public static void Main()
{
double radius;
double circumference;
Console.WriteLine("Enter the value of radius:");
radius = double.Parse(Console.ReadLine());
Console.WriteLine("Circumference :"+Math.Round(getCircumference(radius), 2));
}
}
```

Here,

*getCircumference*is the method to calculate the*circumference*.- We are using this method to calculate the circumference instead of calculating it directly.
- This is a
*public static*method. We can also put it in a separate class and call it from the*Main*method in the*Main class*.

The output of the program will be same.