In this article, we will illustrate **c program to calculate area of circle**. The formula for the area of circle is :

Area_circle = Π * r * r

**where,**

mathematical value of Π is 3.14159.

Please go through following articles of c programming, if you do not already know about these topics :

## simple c program to calculate area of circle

```
#include <stdio.h>
int main() {
float radius, area_circle;
// take radius as input
printf("Enter the radius of circle : ");
scanf("%f", &radius);
area_circle = 3.14 * radius * radius;
printf("Area of circle : %f", area_circle);
return 0;
}
```

**Output**

```
Enter the radius of circle : 10.0
Area of circle : 31.4
```

In this program first, user is asked to enter the value of radius of the circle. After that area is calculated and then displayed.

## C program for calculating area of a circle using function

```
#include <stdio.h>
// function definition to calculate area of circle
int areaOfcircle(int radius_circle){
float area_circle;
area_circle = 3.14 * radius_circle * radius_circle;
return area_circle;
}
int main() {
float radius;
// take radius as input
printf("Enter the radius of circle : ");
scanf("%f", &radius);
printf("Area of circle : %f", areaOfcircle(radius));
return 0;
}
```

**Output**

```
Enter the radius of circle : 10.0
Area of circle : 31.4
```

This program also calculates and display the area of the circle but only difference is a function name `areaOfcirlce()`

is used to calculate area of circle and return it.