Write a program to find area of circle in C

In this post, you will know different C programs to find the area of the circle. As we all know, the area of the circle is the measure of the space or region enclosed inside the circle. In geometry, the area enclosed by a circle of radius r is πr². Here is the simple formula for calculating the area of the circle.

Area = pi * r2

C program to calculate the area of circle using radius

Here is the simple C program to calculate the area of a circle using a radius.

#include <stdio.h>
#include <conio.h>

#define PI 3.141
int main()
{
    float radius, area;
    printf("Enter radius of circle\n");
    scanf("%f", &radius);
    area = PI * radius * radius;
    printf("Area of circle : %0.4f\n", area);
    getch();
    return 0;
}

Enter radius of circle
32
Area of circle : 3216.3840

Enter radius of circle
52
Area of circle : 8493.2637

C program to calculate area of circle using diameter

Diameter is the distance across the circle passing through the center. We can also calculate the area of the circle if we know the diameter. Either, we can divide the diameter by 2 and calculate the area using the above process, like this -

#include <stdio.h>
#include <conio.h>

#define PI 3.141
int main()
{
    float diameter, radius, area;
    printf("Enter diameter of a circle : ");
    scanf("%f", &diameter);
    radius = diameter/2;
    area = PI * radius * radius;

    printf("Area of circle : %0.4f\n", area);
    getch();
    return 0;
}

Enter diameter of a circle : 20
Area of circle : 314.1000

Enter diameter of a circle : 42
Area of circle : 1385.1810

C program to get area Of circle using circumference

The circle's circumference is the distance around the circle. We can easily calculate the area of a circle if we know the circumference using a formula. A= C²⁄ 4π, where C is the circumference. The following C program demonstrates this -

#include <stdio.h>
#include <conio.h>

#define PI 3.141
int main()
{
    float circumference, area;
    printf("Enter the circumference of a circle: : ");
    scanf("%f", &circumference);
    area = (circumference * circumference)/(4 * PI);

    printf("Area of circle : %0.4f\n", area);
    getch();
    return 0;
}

Enter the circumference of a circle: : 23
Area of circle : 42.1044

Enter the circumference of a circle: : 56
Area of circle : 249.6020

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