Program to find area, diameter and circumference of a circle

C Program to find area, diameter and circumference of a circle:

By Ahmad Irshad | Programming Exercises and Solutions > find area, diameter and circumference

Write a C program to find area, diameter, and circumference of a circle by taking radius as an input from user. See the below logic to find area, diameter, and circumference of a circle with step by step.

Required knowledge for this exercise is: 

Basic Input output, Data Type, Arithmetic operators 

Before writing any program you just imagine about output screen first. For example: what input to be given, and output to be displayed. Let's have a look at the below example: 

INPUT:

Enter radius of a circle: 4

OUTPUT:

Area of circle = 50.24 sq. units

Diameter of circle = 8.00 sq. units

Circumference of circle = 25.12 sq. units

Farmula to be used for Circle:

Where, D = diameter | C = Circumference | A = Area | r = Radius | and Value of PI = 3.14

Logic to find area, diameter and circumference of a circle:

1) Print a massage to the user like "Enter radius of a circle:" using printf();

2) Input radius using scanf(); and store it in a variable radius.

3) Now find area, diameter and circumference of a circle using farmula: area = PI * radius * radius,diameter = 2 * radiusand circumference = 2 * PI * radius.

4) At last print the value of area, diameter and circumference. that's it!

Program to find area, diameter, and circumference of a circle: 

1. /* C program to find area, diameter, and circumference of a circle */
   
2. 
   

#include <stdio.h> #define PI 3.14 int main() { float radius, diameter, circumference, area; /* * Input radius of circle from user */ printf("Enter radius of a circle: "); scanf("%f", &radius); /* * Calculate area, diameter and areacircumference of a circle.

* ------------------------------------------------------------------

* Remembeer: Since PI has constant value 3.14 so We need to define

* the value of PI by using pre-processor directive #define PI 3.14 .

*/

area = PI * (radius * radius); // diameter = 2 * radius; circumference = 2 * PI * radius; /* * Print all results */

printf("Area of circle = %.2f sq. units ", area); printf("Diameter of circle = %.2f units \n", diameter); printf("Circumference of circle = %.2f units \n", circumference); return 0; }

Note: #define is preprcessor directive which is used to define canstant value. Such as #define PI 3.14 as you can see in the above program.

Let's rewrite the above program by another way using constant variable M_PI.

Program to find area, diameter, and circumference of a circle: 

1. /* C program to find area, diameter, and circumference of a circle */
   
2. 
   

#include <stdio.h> #include <math.h> // Used for M_PI int main() { float radius, diameter, circumference, area; /* * Input radius of circle from user */ printf("Enter radius of a circle: "); scanf("%f", &radius); /* * Calculate area, diameter and areacircumference of a circle.

* ------------------------------------------------------------------

* Remembeer: Since PI has fixed value 3.14, It is always recommended

* to use constant variable to represent such constant. The constant

* PI is already defined in <math.h> header file with name M_PI.

*/

area = M_PI * (radius * radius); // diameter = 2 * radius; circumference = 2 * M_PI * radius; /* * Print all results */

printf("Area of circle = %.2f sq. units ", area); printf("Diameter of circle = %.2f units \n", diameter); printf("Circumference of circle = %.2f units \n", circumference); return 0; }

Note: M_PI is nothing but a constant variable which is already defined in #include <math.h> deader file

Constant variable: In C programming language, such variables or value which cannot be modified once they are defined. They are fixed values in a program. There can be any types of constant like integer, float, character constant etc.

Visit to know more about constant variable.  

Output:

1. Enter radius of a circle: 4

1. Area of circle = 50.24 sq. units
2. Diameter of circle = 8.00 units
3. Circumference of circle = 25.12 units

In place of constant variable M_PI, You can direcly use 3.14 since the value of PI = 3.14. Have a look at the below statements taken from above program. 

1. /*

* Calculate area, diameter and areacircumference of a circle.

* ------------------------------------------------------------

* Remembeer: Since PI has fixed value 3.14, It is always recommended

* to use constant variable to represent such constant. The constant

* PI is already defined in <math.h> header file with name M_PI.

*/

area = 3.14 * (radius * radius); // diameter = 2 * radius; circumference = 2 * 3.14 * radius;

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