C program to find diameter, circumference and area of circle using function

Write a C program to input radius of circle from user and find diameter, circumference and area of the given circle using function. How to find diameter, circumference and area of a circle using function in C programming.

Example

Input

`Input radius: 10`

Output

```Diameter = 20 units
Circumference = 62.83 units
Area = 314.16 sq. units```

Required knowledge

In previous exercise we learned to declare and use program with single user defined function. Here in this program we will define more than one user-defined functions in a single program.

Declare functions to find diameter, circumference and area of circle

1. First assign a meaningful name to all the three functions. Say function to calculate diameter, circumference and area are - `getDiameter()`, `getCircumference()` and `getArea()` respectively.
2. All the above three functions uses one input i.e. radius of circle to calculate output. Hence all the three function must accept a parameter of `double` or `int` type.
3. Finally, all the three functions returns either `double` or `int` as output. Hence, return type of the function must be either `double` or `int`.

After considering above points function declaration looks like -

``````

Program to find diameter, circumference and area using functions

``````/**
* C program to find diameter, circumference and area of a circle using functions
*/

#include <stdio.h>
#include <math.h> // Used for constant PI referred as M_PI

/* Function declaration */

int main()
{

/* Input radius of circle from user */

dia  = getDiameter(radius);       // Call getDiameter function
circ = getCircumference(radius);  // Call getCircumference function
area = getArea(radius);           // Call getArea function

printf("Diameter of the circle = %.2f units\n", dia);
printf("Circumference of the circle = %.2f units\n", circ);
printf("Area of the circle = %.2f sq. units", area);

return 0;
}

/**
* Calculate diameter of circle whose radius is given
*/
{
}

/**
* Calculate circumference of circle whose radius is given
*/
{
return (2 * M_PI * radius); // M_PI = PI = 3.14 ...
}

/**
* Find area of circle whose radius is given
*/
{
return (M_PI * radius * radius); // M_PI = PI = 3.14 ...
}``````

Output

```Enter radius of the circle: 10
Diameter of the circle = 20.00 units
Circumference of the circle = 62.83 units
Area of the circle = 314.16 sq. units```

Happy coding 😉

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