C Program to Calculate Area Of a Circle

How to write C Program to Calculate the Area Of a Circle with an example?. Before we step into the program, Let’s see the definitions and formulas behind this.

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 the radius).

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

#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;
}

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

The distance around the circle is 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 the 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 the 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 passes through the center, called 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)

#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 c program to find the area of a circle allows the user to insert the diameter value. 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

About Suresh

Suresh is the founder of TutorialGateway and a freelance software developer. He specialized in Designing and Developing Windows and Web applications. The experience he gained in Programming and BI integration, and reporting tools translates into this blog. You can find him on Facebook or Twitter.

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