C Program To Find Area And Circumference Of Circle Using Function

Calculating the area and circumference of a circle is a fundamental geometric task in programming. In this article, you will learn how to write a C program that efficiently calculates these values using custom functions, promoting code reusability and modularity.

Problem Statement

The challenge is to compute the area and circumference of a circle given its radius. A key requirement is to encapsulate the calculation logic within separate functions to enhance code organization and maintainability, rather than performing all computations directly in the main function. This approach makes the code easier to read, debug, and reuse in larger projects.

Example

For a circle with a radius of 5.0 units, the program should produce output similar to the following:

Enter the radius of the circle: 5.0
Area of the circle: 78.54 square units
Circumference of the circle: 31.42 units

Background & Knowledge Prerequisites

To understand this article, readers should be familiar with:

• C Language Basics: Fundamental syntax, data types (e.g., float, double), input/output operations (printf, scanf).
• Functions in C: Defining functions, passing arguments, returning values.
• Math Library: Basic understanding of how to include and use mathematical functions (specifically M_PI for pi) from the header.
• On some compilers (e.g., MSVC), you might need to #define _USE_MATH_DEFINES before including to expose M_PI.
• When compiling with GCC/Clang, link the math library using the -lm flag (e.g., gcc your_program.c -o your_program -lm).

Use Cases or Case Studies

Calculating the area and circumference of a circle is crucial in various real-world applications:

• Engineering Design: Determining the cross-sectional area of pipes, cables, or circular components for stress analysis and material estimation.
• Architecture and Construction: Calculating the amount of material needed for circular foundations, domes, or decorative elements.
• Physics and Astronomy: Solving problems related to orbital mechanics, wave propagation, or the properties of circular objects.
• Computer Graphics and Game Development: Drawing circular shapes, calculating collision detection for circular objects, or determining areas for rendering effects.
• Agriculture: Estimating the area of circular fields for irrigation planning or fertilizer application.

Solution Approaches

We will implement a solution using separate functions for calculating the area and circumference. This approach keeps the code modular and easy to manage.

Approach 1: Using Separate Functions for Area and Circumference

This approach involves defining two distinct functions: one for calculating the area and another for the circumference. Both functions will accept the radius as input and return the calculated value.

// Circle Area and Circumference Calculator
#include <stdio.h>  // Required for input/output operations (printf, scanf)
#include <math.h>   // Required for M_PI constant and mathematical functions

// On some compilers, _USE_MATH_DEFINES is needed to expose M_PI
#ifndef M_PI
    #define M_PI 3.14159265358979323846
#endif

// Function to calculate the area of a circle
// Takes the radius as a double and returns the area as a double
double calculateArea(double radius) {
    return M_PI * radius * radius;
}

// Function to calculate the circumference of a circle
// Takes the radius as a double and returns the circumference as a double
double calculateCircumference(double radius) {
    return 2 * M_PI * radius;
}

int main() {
    // Step 1: Declare a variable to store the radius
    double radius;

    // Step 2: Prompt the user to enter the radius
    printf("Enter the radius of the circle: ");

    // Step 3: Read the radius from the user
    // %lf is used for reading double values with scanf
    scanf("%lf", &radius);

    // Step 4: Call the calculateArea function and store the result
    double area = calculateArea(radius);

    // Step 5: Call the calculateCircumference function and store the result
    double circumference = calculateCircumference(radius);

    // Step 6: Print the calculated area, formatted to two decimal places
    printf("Area of the circle: %.2f square units\\n", area);

    // Step 7: Print the calculated circumference, formatted to two decimal places
    printf("Circumference of the circle: %.2f units\\n", circumference);

    return 0; // Indicate successful program execution
}

Run

Sample Output

Enter the radius of the circle: 7.5
Area of the circle: 176.71 square units
Circumference of the circle: 47.12 units

Stepwise Explanation

1. Include Headers:

• stdio.h is included for standard input/output functions like printf and scanf.
• math.h is included to access mathematical constants and functions, specifically M_PI which represents the value of Pi. A fallback definition for M_PI is also provided in case it's not exposed by default.

1. calculateArea Function:

• This function is defined to take a double type argument, radius.
• It calculates the area using the formula: π * r * r (Pi multiplied by radius squared).
• It returns the calculated area as a double.

1. calculateCircumference Function:

• Similar to calculateArea, this function also takes a double radius.
• It calculates the circumference using the formula: 2 * π * r (2 multiplied by Pi multiplied by radius).
• It returns the calculated circumference as a double.

1. main Function:

• A double variable radius is declared to store the user's input.
• The program prompts the user to enter the radius using printf.
• scanf("%lf", &radius); reads the floating-point value entered by the user and stores it in the radius variable. The %lf format specifier is used for reading double values.
• The calculateArea and calculateCircumference functions are called with the radius as an argument, and their return values are stored in area and circumference variables, respectively.
• Finally, printf is used to display the calculated area and circumference. The %.2f format specifier ensures that the output floating-point numbers are displayed with two decimal places, making the output neat.
• return 0; signifies that the program executed successfully.

Conclusion

By implementing separate functions for area and circumference calculations, we achieve a well-structured and reusable C program. This modular approach not only makes the code cleaner and easier to understand but also promotes good programming practices crucial for developing larger, more complex applications.

Summary

• Functions (calculateArea, calculateCircumference) are used to encapsulate specific logic, improving modularity.
• The header provides the M_PI constant for precise calculations.
• double data type is preferred for calculations involving floating-point numbers to ensure precision.
• Input (scanf) and output (printf) operations are handled using stdio.h.
• The %.2f format specifier in printf is useful for controlling the precision of floating-point output.