C Program To Find Area Of Circle Square And Rectangle Using Function

Calculating the area of different geometric shapes is a fundamental task in programming. Organizing these calculations using functions can significantly improve code readability, reusability, and maintainability. In this article, you will learn how to implement C programs to find the area of a circle, square, and rectangle using separate, well-defined functions.

Problem Statement

In many applications, there's a need to compute the areas of basic geometric shapes like circles, squares, and rectangles. A common challenge arises when these calculations are repeated throughout a program, leading to duplicated code. For instance, a CAD application might need to calculate areas for multiple components, or a simple geometry tool might offer various area computations. Duplicating code for each shape's area calculation makes the program harder to read, debug, and update.

Example

The final program will allow a user to choose a shape and then provide its dimensions to calculate and display the area, like this:

Enter the shape for which to calculate area:
1. Circle
2. Square
3. Rectangle
Enter your choice (1-3): 1
Enter the radius of the circle: 5
Area of the circle with radius 5.00 is: 78.50

Enter the shape for which to calculate area:
1. Circle
2. Square
3. Rectangle
Enter your choice (1-3): 2
Enter the side length of the square: 7
Area of the square with side 7.00 is: 49.00

Background & Knowledge Prerequisites

To understand this article, readers should have a basic understanding of:

• C Programming Basics: Variables, data types (especially float or double for precision).
• Functions: How to declare, define, and call functions, including passing arguments and returning values.
• Standard Input/Output: Using printf() for output and scanf() for input.
• Conditional Statements: Basic if-else or switch statements for menu-driven programs.
• Math Library: Basic knowledge of M_PI constant from for circle calculations.

Use Cases or Case Studies

Area calculations are crucial in various real-world scenarios:

• Construction and Architecture: Determining the amount of material needed for flooring, roofing, or painting rooms and structures.
• Urban Planning: Calculating land usage, green spaces, or paved areas within a city layout.
• Game Development: Collision detection, rendering object sizes, or defining play areas in a game engine.
• Engineering Design: Sizing components, calculating stress distribution over a surface, or estimating fluid flow in pipes.
• Agriculture: Measuring field sizes for crop yield estimation or fertilizer application planning.

Solution Approaches

We will focus on a structured approach using separate functions for each shape's area calculation, integrated into a menu-driven program.

Approach 1: Calculating Area Using Separate Functions

This approach involves creating distinct functions for calculating the area of a circle, square, and rectangle. Each function will take the necessary dimensions as arguments and return the computed area. This promotes modularity and makes the main program cleaner.

• One-line summary: Define and use dedicated functions (areaCircle, areaSquare, areaRectangle) to encapsulate the area calculation logic for each shape.

// Area Calculator using Functions
#include <stdio.h>  // For printf, scanf
#include <math.h>   // For M_PI (pi constant)

// Function to calculate the area of a circle
// Parameters: radius (float)
// Returns: area of the circle (float)
float areaCircle(float radius) {
    return M_PI * radius * radius;
}

// Function to calculate the area of a square
// Parameters: side (float)
// Returns: area of the square (float)
float areaSquare(float side) {
    return side * side;
}

// Function to calculate the area of a rectangle
// Parameters: length (float), width (float)
// Returns: area of the rectangle (float)
float areaRectangle(float length, float width) {
    return length * width;
}

int main() {
    int choice;
    float radius, side, length, width;
    float resultArea;

    // Step 1: Display menu to the user
    printf("Enter the shape for which to calculate area:\\n");
    printf("1. Circle\\n");
    printf("2. Square\\n");
    printf("3. Rectangle\\n");
    printf("Enter your choice (1-3): ");
    scanf("%d", &choice);

    // Step 2: Process user's choice using a switch statement
    switch (choice) {
        case 1:
            printf("Enter the radius of the circle: ");
            scanf("%f", &radius);
            resultArea = areaCircle(radius); // Call the areaCircle function
            printf("Area of the circle with radius %.2f is: %.2f\\n", radius, resultArea);
            break;
        case 2:
            printf("Enter the side length of the square: ");
            scanf("%f", &side);
            resultArea = areaSquare(side); // Call the areaSquare function
            printf("Area of the square with side %.2f is: %.2f\\n", side, resultArea);
            break;
        case 3:
            printf("Enter the length of the rectangle: ");
            printf("Enter the width of the rectangle: ");
            scanf("%f", &length);
            scanf("%f", &width);
            resultArea = areaRectangle(length, width); // Call the areaRectangle function
            printf("Area of the rectangle with length %.2f and width %.2f is: %.2f\\n", length, width, resultArea);
            break;
        default:
            printf("Invalid choice. Please enter a number between 1 and 3.\\n");
            break;
    }

    return 0;
}

Run

• Sample Output:

Enter the shape for which to calculate area:
1. Circle
2. Square
3. Rectangle
Enter your choice (1-3): 1
Enter the radius of the circle: 4.5
Area of the circle with radius 4.50 is: 63.59

Enter the shape for which to calculate area:
1. Circle
2. Square
3. Rectangle
Enter your choice (1-3): 3
Enter the length of the rectangle: 10
Enter the width of the rectangle: 5.5
Area of the rectangle with length 10.00 and width 5.50 is: 55.00

• Stepwise explanation for clarity:

1. Include Headers: stdio.h is included for input/output operations (printf, scanf), and math.h is included to access the M_PI constant (the value of Pi).
2. Define areaCircle Function: This function takes a float radius as input and returns the calculated area using the formula M_PI * radius * radius.
3. Define areaSquare Function: This function takes a float side as input and returns the area using side * side.
4. Define areaRectangle Function: This function takes two float arguments, length and width, and returns their product as the area.
5. main Function:

• It declares variables to store user choice and the dimensions (radius, side, length, width), along with resultArea.
• A menu is displayed to the user using printf.
• scanf reads the user's choice.
• A switch statement handles the user's input:
• Case 1 (Circle): Prompts for radius, calls areaCircle() with the provided radius, and prints the result.
• Case 2 (Square): Prompts for side, calls areaSquare() with the provided side, and prints the result.
• Case 3 (Rectangle): Prompts for length and width, calls areaRectangle() with these values, and prints the result.
• default: Handles invalid choices.
• %.2f in printf formats the floating-point output to two decimal places for better readability.

Conclusion

Using functions to calculate the area of different shapes significantly improves code organization and efficiency. Each function encapsulates a specific piece of logic, making the code easier to understand, test, and reuse. This modular approach is a cornerstone of good programming practices, leading to more robust and maintainable applications.

Summary

• Functions promote code modularity, making programs easier to read and maintain.
• Separate functions (areaCircle, areaSquare, areaRectangle) can be defined for specific tasks.
• Functions take input parameters (e.g., radius, side, length, width) and return a calculated value (the area).
• The main function orchestrates the program flow, often using a menu and conditional statements (switch) to call the appropriate area calculation function based on user input.
• Using float or double data types ensures precision for geometric calculations, and M_PI from math.h provides an accurate value for Pi.