Example: How to Find Area of a Circle with Diameter in C using M_PI Constant

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// How to Find Area of a Circle with Diameter in C using M_PI Constant
#include <stdio.h>
#include <math.h> // To import M_PI constant

int main() {
    float r, d = 0, c = 0, a = 0;
    // r = radius, d = diameter, c = circumference, a = area

    printf("Enter the radius of the circle::\n");
    scanf("%f", &r);

    // Calculation of diameter, circumference, and area
    d = 2 * r;
    c = 2 * M_PI * r;
    a = M_PI * (r * r);

    // It will print the final output
    printf("\n");
    printf("Diameter      :: = %f units \n", d);
    printf("Circumference :: = %f units \n", c);
    printf("Area          :: = %f sq. units ", a);
    return 0;
}