These are the different ways to calculate the area and circumference of the circle in C programming.

#include<stdio.h>
#include<conio.h>
#define pi 3.14

void main()
{
  int r;
  float a, c;

  printf("ntenter value of radius=");
  scanf("%d",&r);

  a= pi*r*r;
  c=2*pi*r;

  printf("tArea = %.2fn",a);
  printf("tCircumference = %.2fn",c);

  getch();

}

Output

 You can also perform this calculate by defining pi as float value.   

C Code

#include<stdio.h>
#include<conio.h>

void main()
{
  int r;
  float a, c;
  float pi=3.14;

  printf("ntenter value of radius=");
  scanf("%d",&r);

  a= pi*r*r;
  c=2*pi*r;

  printf("tArea = %.2fn",a);
  printf("tCircumference = %.2fn",c);

  getch();

}

Output

 You can also perform this calculation by putting value 

C Code

#include<stdio.h>
#include<conio.h>

void main()
{
  int r;
  float a, c;

  printf("ntenter value of radius=");
  scanf("%d",&r);

  a= 3.14*r*r;
  c=2*3.14*r;

  printf("tArea = %.2fn",a);
  printf("tCircumference = %.2fn",c);

  getch();

}