# C Program to Calculate Area of a Circle

Here is a C program to find the area and circumference of a circle. A circle is a simple geometrical shape. A circle is a set of all points in a 2D plane that are at a given distance from a given point called centre. A circle can be uniquely identified by it's center co-ordinates and radius.

• Center of a Circle is a point inside the circle and is at an equal distance from all of the points on its circumference.
• Radius is the length of the a segment joining the centre of the circle to any point on the circle.
• Diameter is the length of the a segment passing through centre of the circle and joining two points on edge. Diameter is twice of Radius.

The area of circle is the amount of two-dimensional space taken up by a circle. The area of a circle can be calculated by placing the circle over a grid and counting the number of squares that circle covers. Different shapes have different ways to find the area.
We can compute the area of a Circle if you know its radius.

Area of Circle = PI X Radius X Radius.
Where PI is a constant which is equal to 22/7 or 3.141(approx)
Area is measured in square units.

Circumference is the linear distance around the edge of a circle. It is the length of the curved line which defines the boundary of a circle. The perimeter of a circle is called the circumference.

We can compute the circumference of a Circle if you know its radius.
• Circumference or Circle = 2 X PI X Radius
We can also compute the circumference of a Circle if you know its diameter.
• Circumference or Circle = PI X Diameter

## C Program to find the area of the circle

```#include <stdio.h>

#define PI 3.141

int main(){

printf("Enter radius of circle\n");

printf("Area of circle : %0.4f\n",
area);

return 0;
}
```
In above program, we first take radius of a circle as an input from user using scanf function and store it in floating point variable named "radius". Now, we calculate the area of circle(PI X radius X radius) and store it in variable area. Then we print the area of circle on screen using printf function.

Output
```Enter radius of circle
5
Area of circle : 78.5250
```

## C Program to find the area of a circle using pow function

We can use pow function of math.h header file to calculate Radius^2(Radius square) instead of multiplying Radius with itself. double pow(double a, double b) returns a raised to the power of b (a^b). Below program uses pow function to calculate the area of circle.

```#include <stdio.h>
#include <math.h>

#define PI 3.141

int main(){

printf("Enter radius of circle\n");

area = PI*pow(radius, 2);
printf("Area of circle : %0.4f\n", area);

return 0;
}
```

Output
```Enter radius of circle
3
Area of circle : 28.2690
```

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