 # C Program to find area of a circle with given radius

For a better understanding of this C program example, we always recommend you to learn the basic topics of C programming listed below:

## How to find the area of a circle given radius

In this C program, we need to find the area of a circle with the radius given. A circle is a shape that has no corners, and the area of the circle is defined as the region that is inside that closed shape.

In a circle, we have two important measurements which are

1. Radius r: Radius is the length of the line that joins any point on the circle and its center.
2. Diameter d: The diameter of a circle can be defined as the double of the radius, that is a line that connects two points on the circle which passes through the center. The area of a circle is calculated using the formula,  Π r2, where, r is the radius.

Let's take an example of a circle with a diameter of 4. which means the circle has a 4 cm length between the longest points. then its radius will be 2.

Now we can calculate the area by using the formula Π r2

• "Π * 2 * 2"
• that is "Π* 4"
• The value of Π is 3.14
• then the final area will be 3.14 * 4 = 12.56.

## How we calculate the area of the circle with #define using the C program

• Let's check how we implement the above logic in the C program.
• We are defining the value of 'pi' as 3.14 as it is a constant value.
• To apply the formula that use to find the ara of the circle we are using `pow function` which is defined in the` math` library for calculating the square of the radius, and then we are using precision to the float value to print only two decimals after the dot.

## ALGORITHM

STEP 1: Import the header file libraries into the C program to use built-in functions such as `stdio`, `conio`, and `math.h`.

STEP 2: Define the value of 'pi' as '3.14' using C programming syntax.

STEP 3: Open the main() to start the program in the C language.

STEP 4: After initializing the variables for radius and area using `float` data type, accept the value of radius from the user using `printf` and `scanf` functions in C.

STEP 5: Calculate the area of the circle using the formula 'pi * pow (radius,2)'.

STEP 6: Print the result using `printf` statement, Here we use 5.2f which adds Precision in the float data type. which means it prints only that much decimal value as result.

## C Source Code

```                                          ```#include <stdio.h>
#include <math.h>
#define PI 3.142

void main()
{
printf("Enter the radius of a circle\n");
area = PI * pow (radius,2);
printf ("Area of a circle = %5.2f\n", area);
}```
```

## OUTPUT

```RUN 1
=======
Enter the radius of a circle
3.2
Area of a circle = 32.17

RUN 2
========
Enter the radius of a circle
6
Area of a circle = 113.11```
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