Write A C Program To Find Area Of Circle Using User Defined Function

In this article, you will learn how to write a C program to calculate the area of a circle using a user-defined function, enhancing modularity and reusability in your code.

Problem Statement

Calculating the area of a circle is a fundamental geometric problem. The challenge lies in efficiently computing the area for various radii, particularly when this calculation might be needed multiple times within a larger program or across different parts of a system. Using a dedicated function for this task promotes cleaner code and easier maintenance.

Example

Consider a circle with a radius of 5.0 units. The program should output its area, which would be approximately 78.54 square units.

Enter the radius of the circle: 5.0
The area of the circle with radius 5.00 is: 78.54

Background & Knowledge Prerequisites

To understand this article, readers should be familiar with:

• C Language Basics: Fundamental syntax, variable declaration, and basic input/output operations.
• Functions in C: How to declare, define, and call user-defined functions, including parameter passing and return types.
• Data Types: Understanding double for floating-point numbers.
• Constants: Using const or #define for fixed values like PI.
• Standard I/O Library (stdio.h): For input (scanf) and output (printf).

Use Cases or Case Studies

Calculating the area of a circle is a common operation with various practical applications:

• Engineering Design: Determining the cross-sectional area of pipes, wires, or circular components in mechanical or electrical engineering.
• Architecture and Construction: Calculating the surface area for circular foundations, domes, or decorative elements.
• GIS and Mapping: Estimating the coverage area of circular zones, such as the effective range of a sensor or a wireless signal.
• Game Development: Calculating collision areas for circular objects or determining the radius of effect for a circular explosion.
• Manufacturing: Quality control checks for circular parts, ensuring they meet specified area tolerances.

Solution Approaches

While directly calculating the area within main is possible, using a user-defined function is the recommended approach for better code organization.

Calculating Circle Area with a User-Defined Function

This approach involves creating a separate function responsible solely for computing the circle's area. This function takes the radius as input and returns the calculated area.

• Approach Title: Calculating Circle Area with a User-Defined Function
• One-line summary: Encapsulate the area calculation logic within a dedicated function, making the main program cleaner and the calculation reusable.

// Calculate Area of Circle Using User-Defined Function
#include <stdio.h> // Required for input/output operations

// Define the constant PI for calculations
const double PI = 3.14159;

// Function to calculate the area of a circle
// It takes a double 'radius' as input and returns the calculated area as a double.
double calculateCircleArea(double radius) {
    // Step 1: Calculate the area using the formula: Area = PI * radius * radius
    double area = PI * radius * radius;
    // Step 2: Return the calculated area
    return area;
}

int main() {
    // Step 1: Declare a variable to store the radius entered by the user
    double radius;
    // Step 2: Declare a variable to store the calculated area
    double area;

    // Step 3: Prompt the user to enter the radius
    printf("Enter the radius of the circle: ");
    // Step 4: Read the radius from the user input
    // Use %lf for reading double values
    scanf("%lf", &radius);

    // Step 5: Call the user-defined function to calculate the area
    // Pass the 'radius' to the function and store the returned value in 'area'
    area = calculateCircleArea(radius);

    // Step 6: Display the calculated area to the user
    // Use %.2lf to print the double value with two decimal places
    printf("The area of the circle with radius %.2lf is: %.2lf\\n", radius, area);

    return 0; // Indicate successful program execution
}

Run

• Sample Output:

Enter the radius of the circle: 7.5
The area of the circle with radius 7.50 is: 176.71

• Stepwise Explanation for Clarity:

1. Include Header: The stdio.h header is included for standard input (scanf) and output (printf) functions.
2. Define PI: A const double variable PI is defined with an approximate value for π. Using const ensures its value cannot be accidentally changed.
3. calculateCircleArea Function Definition:

• It's declared to return a double (the area) and accept a double parameter (the radius).
• Inside the function, the area is calculated using the formula PI * radius * radius.
• The calculated area is then returned to the calling function.

1. main Function:

• Variable Declaration: double radius and double area are declared to hold the user's input and the computed result, respectively.
• User Input: printf prompts the user for the radius, and scanf("%lf", &radius) reads the double value entered by the user.
• Function Call: calculateCircleArea(radius) is called, passing the radius as an argument. The returned value (the calculated area) is stored in the area variable.
• Display Result: printf displays the radius and the calculated area, formatted to two decimal places using %.2lf.
• Return 0: Indicates that the program executed successfully.

Conclusion

Using a user-defined function to calculate the area of a circle is an excellent practice for writing modular and maintainable C code. This approach isolates the specific calculation logic, making the main function cleaner, improving code readability, and allowing the area calculation to be easily reused in different parts of a program or even across multiple programs without duplicating code.

Summary

• The problem involves calculating a circle's area, ideally using a user-defined function.
• Prerequisites include basic C syntax, functions, double data type, and stdio.h.
• Common use cases span engineering, architecture, gaming, and manufacturing.
• The primary solution involves defining a double calculateCircleArea(double radius) function.
• This function encapsulates the formula PI * radius * radius and returns the result.
• The main function handles user input, calls calculateCircleArea, and displays the formatted output.
• This structured approach enhances code reusability, readability, and maintainability.