C Program to Calculate Area Of a Circle

How to write C Program to Calculate Area Of a Circle with example?. Before we step into the program, Let see the definitions and formulas behind the Area Of a Circle. The area of a circle is the number of square units inside the circle. The standard formula to calculate the area of a circle is A=πr². 

C Program to Calculate Area Of a Circle using Radius

If we know the radius, then we can calculate the area of a circle using the formula: A=πr² (Here A is the area of the circle and r is radius).

In this C program, we allow the user to enter the radius, and We defined pi as a global variable and assigned value as 3.14. Next, this C program will find the area of the circle and circumference of a circle as per the formula.

/* C Program to Calculate Area Of a Circle using Radius */

#include<stdio.h>

#define PI 3.14

int main()
{
  float radius, area, circumference;

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

  area = PI*radius*radius; 
  circumference = 2* PI*radius;

  printf("\n Area Of a Circle = %.2f\n", area);
  printf("\n Circumference Of a Circle = %.2f\n", circumference);

  return 0;
}

c area of a circle output

 Please Enter the radius of a circle
6

 Area Of a Circle = 113.04

 Circumference Of a Circle = 37.68

C Program to Calculate Area Of a Circle using Circumference

Distance around the circle called the circumference. If you know the circumference, we can calculate the area of a circle using the formula: A= C²⁄ 4π (Here C is circumference)

/* C Program to Calculate Area Of a Circle using Circumference */

#include <stdio.h>
#include <math.h>

int main()
{
  float area, circumference;

  printf("\n Please Enter the Circumference of a circle \n");
  scanf("%f", &circumference);

  /* We can use M_PI instead of defining PI 
  by adding math.h header file */
  area = (circumference * circumference) /(4* M_PI);

  printf("\n Area Of Circle = %.2f\n", area);
  return 0;
}

In this program, we included one more header file called <math.h>, It allows using pi without declaring it. This program allows the user to enter the value of circumference. Then this C Program will find the area of a circle as per the formula.

 Please Enter the Circumference of a circle 
26

 Area Of Circle = 53.79

C Program to Calculate Area Of a Circle using Diameter

The distance across the circle passing through the center, called as diameter. If we know the diameter, we can calculate the area of a circle using the formula: A=π/4*D² (D is the diameter)

/* C Program to Calculate Area Of a Circle using Diameter */

#include<stdio.h>

main()
{
  float PI = 3.14;
  float area1, area2, diameter, radius;

  printf("\nPlease Enter the Diameter of a circle\n");
  scanf("%f", &diameter);

  area1 = (PI/4)* (diameter*diameter); 
  //diameter = 2 * radius
  //radius = diameter/2
  radius = diameter/2;
  area2 = PI*radius*radius;

  printf("\nArea of Circle using direct formula = %.2f\n", area1);
  printf("\nArea of Circle Using Method 2 = %.2f\n", area2);

  return 0; 
}

This program allows the user to insert the value of the diameter. Then it calculates the area of a circle as per the formula we shown above. 

We also mentioned other approaches.
diameter = 2 * radius
radius = diameter/2
area = π*radius*radius

C Program to Calculate Area Of a Circle using Diameter

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