# C Program to find circumference, diameter and area of a circle

Category: C Program

Learn how to write a C program to calculate the circumference, diameter, and area of a circle using functions. This article provides a complete explanation and code example, highlighting the benefits of using functions in C programming.

Calculating the circumference, diameter, and area of a circle is a common problem in geometry and mathematics. These calculations are fundamental for various applications, from simple geometry problems to complex engineering designs. In this article, we will write a C program that calculates these three properties of a circle using separate functions for each calculation. This approach will help us understand the modularity and reusability of functions in C programming.

## Understanding the Properties of a Circle

To compute the circumference, diameter, and area of a circle, we need to understand the following formulas:

1. Diameter (D): The diameter of a circle is twice the radius.

D = 2 x r

2. Circumference (C): The circumference is the distance around the circle and is calculated using the formula:

C = 2 x pi x r

3. Area (A): The area is the space enclosed by the circle and is given by:

A = pi x r^2

Where r is the radius of the circle and Π (Pi) is approximately 3.14159.

## Write a C Program to find circumference, diameter and area of a circle

We will implement a C program that defines three functions: `calculateDiameter`, `calculateCircumference`, and `calculateArea`. Each function will perform one of the calculations based on the radius provided by the user.

``````#include <stdio.h>
#define PI 3.14159

// Function to calculate the diameter of a circle
}

// Function to calculate the circumference of a circle
return 2 * PI * radius;
}

// Function to calculate the area of a circle
}

int main() {

// Input the radius from the user
printf("Enter the radius of the circle: ");

// Call the functions to calculate diameter, circumference, and area

// Output the results
printf("Diameter of the circle: %.2lf\n", diameter);
printf("Circumference of the circle: %.2lf\n", circumference);
printf("Area of the circle: %.2lf\n", area);

return 0;
}
``````

Output

``````Enter the radius of the circle: 5
Diameter of the circle: 10.00
Circumference of the circle: 31.42
Area of the circle: 78.54
``````

## Explanation of the Code

1. Constants and Libraries:
• We define `PI` as 3.14159, which is used in the formulas for circumference and area.
2. Function `calculateDiameter`:
• Takes the radius as input and returns the diameter, calculated as `2 * radius`.
3. Function `calculateCircumference`:
• Takes the radius as input and returns the circumference, calculated as `2 * PI * radius`.
4. Function `calculateArea`:
• Takes the radius as input and returns the area, calculated as `PI * radius * radius`.
5. Main Function `main`:
• The user is prompted to enter the radius of the circle.
• The functions are called to compute the diameter, circumference, and area, and their results are stored in respective variables.
• The results are then printed to the console.