Question

How to calculate the area, diameter, and circumference of a circle in C

Answer 1

#include <stdio.h>
 
int main(void)
{
	int radius = 3;
	float PI = 3.14f;
 
	float area = PI * radius * radius;
	printf("Area = %.2f\n", area);
 
	float diameter = 2 * radius;
	printf("Diameter = %.2f\n", diameter);
 
	float circumference = 2 * PI * radius;
	printf("Circumference = %.2f\n", circumference);
     
    return 0;
}

 
/* 
run:

Area = 28.26
Diameter = 6.00
Circumference = 18.84

*/

 

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Answer 2

#include <stdio.h>
#include <stdbool.h>

// Define PI safely for cross-platform compatibility if not already defined
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif

// Structure to hold all calculated circle metrics
typedef struct {
    double diameter;
    double circumference;
    double area;
} CircleMetrics;

/**
 * @brief Calculates the diameter, circumference, and area of a circle.
 * @param radius The radius of the circle (must be non-negative).
 * @param result Pointer to a CircleMetrics struct to store the results.
 * @return true if calculation is successful, false if the radius is invalid.
 */
bool calculate_circle_metrics(double radius, CircleMetrics *result) {
    // Guard clause: radius cannot be negative and pointer must not be null
    if (radius < 0.0 || result == NULL) {
        return false;
    }

    // Perform calculations
    result->diameter = 2.0 * radius;
    result->circumference = 2.0 * M_PI * radius;
    
    // Multiplication (radius * radius) is more efficient than pow(radius, 2)
    result->area = M_PI * (radius * radius);

    return true;
}

int main(void) {
    double radius = 3.0;
    CircleMetrics metrics;

    // Call the function and handle the success/failure status
    if (calculate_circle_metrics(radius, &metrics)) {
        printf("Radius: %.2f\n", radius);
        printf("Diameter: %.2f\n", metrics.diameter);
        printf("Circumference: %.2f\n", metrics.circumference);
        printf("Area: %.2f\n", metrics.area);
    } else {
        fprintf(stderr, "Error: Radius cannot be negative.\n");
        return 1;
    }
}


/*
run:

Radius: 3.00
Diameter: 6.00
Circumference: 18.85
Area: 28.27

*/

 

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