How would we write a program that calculates the area of a circle and displays the result?

Answer 1

The area of a circle is calculated as πd^2, where π is the constant ratio between the diameter of a circle and its circumference, d is the diameter of the circle and ^2 is the square of their product.

In programming languages where the value of π is not built-in, we must define it. To ensure the maximum possible precision across all implementations of the language, π is typically expressed as arctan (1) * 4.

In C Programming, we'd define this constant as follows:

const double PI = atan(1.0) * 4.0; // global constant: e.g., 3.14159265359...

From this we can implement a function to compute the area of a circle:

double area_of_circle (double diameter) { return pow (PI * diameter, 2); }

Note that the atan() and pow() functions are both defined in the C standard library header or in if using C++.

Answer 2

The details vary, depending on the programming language; but the main steps are the following:
* Ask the user to specify the radius. Assign the answer to variable "radius".
* Calculate the area, as area = radius * radius * pi
* Show the result

Answer 3

Ask for input of radius, RWait until R is input
Read R

Calculate A = pi*R*R

Output A.