Write a C program to input radius of a circle from user and find diameter, circumference and area of the circle. How to calculate diameter, circumference and area of a circle whose radius is given by user in C programming. Logic to find diameter, circumference and area of a circle in C.
Example
Input
Enter radius: 10
Output
Diameter = 20 units Circumference = 62.79 units Area = 314 sq. units
Required knowledge
Fundamentals of C, Data types, Talking user input in C
Properties of circle
Diameter, circumference and area of a circle formula is given by -
Where r is radius of the circle.
Logic to find diameter, circumference and area of circle
Below is the step by step descriptive logic to find diameter, circumference and area of a circle -
- Read radius of circle from user. Store it in a variable say radius.
- Apply the formulas to compute diameter, circumference and area - diameter = 2 * radius, circumference = 2 * 3.14 * r and area = 3.14 * r * r.
- Print all resultant values diameter, circumference and area.
Let us now code the solution
Program to find diameter, circumference and area of circle
/**
* C program to calculate diameter, circumference and area of circle
*/
#include <stdio.h>
int main()
{
float radius, diameter, circumference, area;
/*
* Input radius of circle from user
*/
printf("Enter radius of circle: ");
scanf("%f", &radius);
/*
* Calculate diameter, circumference and area
*/
diameter = 2 * radius;
circumference = 2 * 3.14 * radius;
area = 3.14 * (radius * radius);
/*
* Print all results
*/
printf("Diameter of circle = %.2f units \n", diameter);
printf("Circumference of circle = %.2f units \n", circumference);
printf("Area of circle = %.2f sq. units ", area);
return 0;
}
Important note: The above program contains a constant value PI. It is always advisable to use a constant variable to represent such types of constants. The constant PI is defined in math.h header file as M_PI. Let us rewrite the above program using constant value.
Program to find diameter, circumference and area of circle using PI constant
/**
* C program to calculate diameter, circumference and area of circle
*/
#include <stdio.h>
#include <math.h> //Used for PI referred as M_PI
int main()
{
float radius, diameter, circumference, area;
/*
* Input radius of circle from user
*/
printf("Enter radius of circle: ");
scanf("%f", &radius);
/*
* Calculate diameter, circumference and area of circle
*/
diameter = 2 * radius;
circumference = 2 * M_PI * radius;
area = M_PI * (radius * radius);
/*
* Print all results
*/
printf("Diameter of circle = %.2f units \n", diameter);
printf("Circumference of circle = %.2f units \n", circumference);
printf("Area of circle = %.2f sq. units ", area);
return 0;
}
Important note: C doesn't provides any exponential operator. Hence never play with operations like radius ^ 2 to find power of any variable or to evaluate exponents.
- Read more if you need to evaluate exponents. C program to find power of any number x^y
Enter radius of circle: 10 Diameter of circle = 20.00 units Circumference of circle = 62.79 units Area of circle = 314.00 sq. units
Note: %.2f is used to print the fractional value up to two decimal places. You can also use %f to print up to default 6 decimal places.
Happy coding ;)