# C Program to Calculate Area and Circumference of a Circle

Before going to the program first let us see how to calculate Area and Circumference of a Circle?

To calculate Area and Circumference of a Circle we should know the formulas for Area of a Circle and Circumference of a Circle.

So the formulas are:

Circumference of a Circle = 2 × π × Radius

Note: The value of π(pi) is 3.14.

Example: Let the value of radius be 5, then

Area of a Circle = 3.14 × 5 × 5 = 78.5

Circumference of a Circle = 2 × 3.14 × 5 = 31.4

## Program code to calculate Area and Circumference of a Circle in C:

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

void main()
{
int r;
float area, cir;
clrscr();

scanf("%d", &r);

area = 3.14 * r * r;
cir = 2 * 3.14 * r;

printf("\n Area of a Circle : %.2f ", area);
printf("\n Circumference of a Circle: %.2f ", cir);

getch();
}
```

## Explanation:

• First the computer reads the value of radius from the user and stores it in the “r” variable using the following lines:
```printf("Enter radius of circle: ");
scanf("%d", &r);
```

Note: %d is used to read the Integer value.

• Then using the formulas the Area and Circumference of a Circle is calculated and stored in the “area” and “cir” variables respectively using the following lines:
```area = 3.14 * r * r;
cir = 2 * 3.14 * r;
```
• Finally the Area and Circumference of a Circle is printed on the screen using the following lines:
```printf("\n Area of a Circle : %.2f ", area);
printf("\n Circumference of a Circle: %.2f ", cir);
```

Note: %.2f is used to print the floating-point value with only 2 decimal places.

## Output: 