# C Program To Calculate Circumference of Circle

By | June 30, 2019

Q: Write a C Program To Calculate Circumference of Circle. Input radius of the circle from the user at run time. Use the formula:

circumference of circle = 2 * PI * radius

## The Logic Behind C Program to Find Circumference of Circle

This is a simple C program using formula calculation technique. The basic formula calculation involves writing C expressions.

### Convert Circumference of Circle Formula into C Expression

The formula to find circumference of the circle is given as:

circumference of circle = 2 x PI x R

where PI is a popular mathematical constant having the value 3.1415.

And R stands for radius of the circle.

We convert this formula to C expression as under:

circumference = 2 * PI * radius;

### How to define constant PI in a C Program

We may use #define pre processor directive to dfine a constant in C language, normally before the start of main() function.

#### Syntax of #define To deifine a Constant in C Program

#define NMAE value

Example:

#define PI 3.1415 C Program To Calculate Circumference of Circle

## The source code of C program to compute circumference of circle

```/*
C Program to
find the circumference of a circle
with formula 2.PI.R
*/

#include<stdio.h>
#define PI 3.1415
int main()
{ 