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

Diameter (D): The diameter of a circle is twice the radius.
D = 2 x r

Circumference (C): The circumference is the distance around the circle and is calculated using the formula:
C = 2 x pi x r

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
double calculateDiameter(double radius) {
return 2 * radius;
}
// Function to calculate the circumference of a circle
double calculateCircumference(double radius) {
return 2 * PI * radius;
}
// Function to calculate the area of a circle
double calculateArea(double radius) {
return PI * radius * radius;
}
int main() {
double radius, diameter, circumference, area;
// Input the radius from the user
printf("Enter the radius of the circle: ");
scanf("%lf", &radius);
// Call the functions to calculate diameter, circumference, and area
diameter = calculateDiameter(radius);
circumference = calculateCircumference(radius);
area = calculateArea(radius);
// 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
 Constants and Libraries:
 We define
PI
as 3.14159, which is used in the formulas for circumference and area.
 We define
 Function
calculateDiameter
: Takes the radius as input and returns the diameter, calculated as
2 * radius
.
 Takes the radius as input and returns the diameter, calculated as
 Function
calculateCircumference
: Takes the radius as input and returns the circumference, calculated as
2 * PI * radius
.
 Takes the radius as input and returns the circumference, calculated as
 Function
calculateArea
: Takes the radius as input and returns the area, calculated as
PI * radius * radius
.
 Takes the radius as input and returns the area, calculated as
 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.