C Program to find Diameter, Circumference, and Area Of a Circle

How to write a C Program to find the Diameter, Circumference, and Area Of a Circle using Functions with examples? The mathematical formulas behind these calculations are:

1. Diameter of a Circle = 2r = 2 * radius
2. Circumference of a Circle = 2πr = 2 * π * radius
3. Area of a circle is: A = πr² =  π * radius * radius

C Program to find Diameter, Circumference, and Area Of a Circle

This program allows the user to enter the radius of a circle. Using that radius value, this program will find the Diameter, Circumference, and Area Of a Circle

TIP: Please refer Program to Calculate Area article to understand the various Programming ways to calculate the same.

 #include<stdio.h>
 
#define PI 3.14
 
int main()
{
  float radius, area, circumference, diameter;
 
  printf("\n Please Enter the radius of a circle : ");
  scanf("%f",&radius);
 
  diameter = 2 * radius;
  circumference = 2 * PI * radius;
  area = PI * radius * radius; 
 
  printf("\n Diameter Of a Circle = %.2f\n", diameter);
  printf("\n Circumference Of a Circle = %.2f\n", circumference);
  printf("\n Area Of a Circle = %.2f\n", area);
 
  return 0;
}

C Program to find Diameter, Circumference, and Area Of a Circle using Functions

In this program, we are using Functions that find the Diameter, Circumference, and Area Of a Circle. Remember, you have to include math.h library to use M_PI. Otherwise, manually define the PI value as we did in the first example.

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

double find_Diameter(double radius);
double find_Circumference(double radius);
double find_Area(double radius);

int main()
{
  float radius, area, circumference, diameter;
 
  printf("\n Please Enter the radius of a circle : ");
  scanf("%f",&radius);
 
  diameter = find_Diameter(radius);
  circumference = find_Circumference(radius);
  area = find_Area(radius); 
 
  printf("\n Diameter Of a Circle = %.2f\n", diameter);
  printf(" Circumference Of a Circle = %.2f\n", circumference);
  printf(" Area Of a Circle = %.2f\n", area);
 
  return 0;
}

double find_Diameter(double radius)
{
   return 2 * radius;
}

double find_Circumference(double radius)
{
   return 2* M_PI * radius;
}
double find_Area(double radius)
{
   return M_PI * radius * radius;
}

From the above code snippet, you can see we created three functions.

• double find_Diameter(double radius) function to calculate the Diameter of a circle.
• double find_Circumference(double radius) function to calculate the Circumference of a circle.
• And double find_Area(double radius) function to find the Area of a circle.
• Next, we called those functions in the main() program to calculate those values.

When the compiler reaches the above-specified functions in the main() program, the compiler will immediately jump to their respective function definitions.

 Please Enter the radius of a circle : 10

 Diameter Of a Circle = 20.00
 Circumference Of a Circle = 62.83
 Area Of a Circle = 314.16