- Write a C program to find the area and circumference of a circle.
- Write a C program to find area 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

/* * C Program to calculate area of a circle */ #include <stdio.h> #include <conio.h> #define PI 3.141 int main(){ float radius, area; printf("Enter radius of circle\n"); scanf("%f", &radius); /* Area of Circle = PI x Radius X Radius */ area = PI*radius*radius; printf("Area of circle : %0.4f\n", area); getch(); 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.

**Program 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.

/* * C Program to calculate area of a circle * using pow function */ #include <stdio.h> #include <math.h> #include <conio.h> #define PI 3.141 int main(){ float radius, area; printf("Enter radius of circle\n"); scanf("%f", &radius); /* Area of Circle = PI x Radius X Radius */ area = PI*pow(radius, 2); printf("Area of circle : %0.4f\n", area); getch(); return 0; }

**Program Output**

Enter radius of circle 3 Area of circle : 28.2690

### C Program to calculate circumference of the circle

Below program calculates the circumference of a circle by taking radius of circle as input from user. We can also find circumference of a circle from diameter, as diameter of a circle is twice of radius.

Below program first take radius of a circle as input from user and then calculate circumference(perimeter) of a circle as 2 X PI X Radius. It then prints the result on screen using printf function.

/* * C Program to find circumference of a circle */ #include <stdio.h> #include <conio.h> #define PI 3.141 int main(){ float radius, circumference; printf("Enter radius of circle\n"); scanf("%f", &radius); /* Circumference of Circle =2 x PI x Radius */ circumference = 2*PI*radius; printf("Circumference of circle : %0.4f\n", circumference); getch(); return 0; }

**Program Output**

Enter radius of circle 3.0 Circumference of circle : 18.8460

**Properties of Circle**

- Diameter is the longest chord of a circle.
- A triangle inside a semi-circle with diameter as one site is always a right angles triangle.
- A tangent to a circle is at right angles to the radius at the point of intersection.
- The length of arc of a circle is proportional to the angle subtended by the arc at the center.
- The equation of a circle whose center is at (0,0) and radius R is x
^{2}+ y^{2}= R^{2}.