pi – Circumference and Area – Computer Science by Example

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pi – Circumference and Area

Given the radius of a circle, calculate its circumference and area.

diagram showing the circumference and area of a circle

The circumference of a circle with radius r is given by 2 × π × r or two times pi times the radius.

The area of a circle with radius r is given by π × r ² or pi times the square of the radius.

The number π, or pi, is a mathematical constant with an irrational value of 3.141 592 653 …

Input and Output

Each line of input contains a decimal value r indicating the radius.

0 < r < 10000.0

For each line of input, your program should produce two numbers, c and a indicating the circumference and area. They should be rounded to two decimal places.

Input is terminated by the end-of-file (EOF).

Example input

Example output

6.28 3.14
75.40 452.39
41.47 136.85
1.00 0.08

Functions `circumference` and `area`

To reach a full score your program should implement two functions circumference and area. Each should take a double-precision floating point number and return a double-precision floating point number. Please see the information for your programming language of choice:

C: double circumference(double r); and double area(double r);
Python: def circumference(r): and def circumference(r):
Haskell: circumference :: Double -> Double and area :: Double -> Double
C++: double circumference(double r); and double area(double r);
C#: public static double Circumference(double r) and public static double Area(double r)
Java: public static double circumference(double r) and public static double area(double r) in a public class Pi
JavaScript: function circumference(r), function area(r)
Lua: function circumference (r) and function area (r)
Ruby: def circumference(r) and def area(r)

Scoring

1/6: works for the above example but with an incorrect output format
2/6: works for the above example with the correct output format
3/6: works for circles with an integral radius
4/6: works for circles with fractional radiuses
5/6: works for edge cases
6/6: implements circumference and area

Hints

The value of π (pi). The value of π (pi) is a real number so the only way to represent it as a floating point value is to use an approximation. Although you can use a hardcoded value of 3.141592653589793 for π it is better to use the one provided by your programming language of choice:
- in C, use M_PI from math.h;
- in Python, use pi from the math module (a.k.a.: math.pi);
- in Haskell use pi from the Prelude.

try first: mult

try next: oddeven order

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