Kotlin Program to Find Area of Circle

To find the area of a circle in Kotlin, use val area = Math.PI * radius * radius where radius is the circle's radius.

Examples

Inputradius = 0

OutputArea of circle is 0.0

Inputradius = 5

OutputArea of circle is 78.53981633974483

Inputradius = 10.5

OutputArea of circle is 346.3605900582744

How to Think About It

To find the area of a circle, you need the radius. The formula is area = π × radius × radius. First, get the radius value, then multiply it by itself and by π (pi).

Algorithm

1

Get the radius value from the user or set it directly.

2

Calculate the area using the formula area = π × radius × radius.

3

Print or return the calculated area.

Code

kotlin

fun main() {
    val radius = 5.0
    val area = Math.PI * radius * radius
    println("Area of circle is $area")
}

Output

Area of circle is 78.53981633974483

Dry Run

Let's trace the example where radius = 5.0 through the code

1

Set radius

radius = 5.0

2

Calculate area

area = 3.141592653589793 * 5.0 * 5.0 = 78.53981633974483

3

Print result

Output: Area of circle is 78.53981633974483

radius	area
5.0	78.53981633974483

Why This Works

Step 1: Using the radius

The radius is the distance from the center of the circle to its edge, needed for the area calculation.

Step 2: Applying the formula

The formula area = π × radius × radius calculates the space inside the circle.

Step 3: Using Math.PI

Kotlin's Math.PI provides a precise value of π for accurate calculation.

Alternative Approaches

Using a function to calculate area

kotlin

fun areaOfCircle(radius: Double): Double {
    return Math.PI * radius * radius
}

fun main() {
    val radius = 7.0
    println("Area of circle is ${areaOfCircle(radius)}")
}

This approach improves code reuse and clarity by separating calculation from input/output.

Using Kotlin's kotlin.math.PI constant

kotlin

import kotlin.math.PI

fun main() {
    val radius = 3.0
    val area = PI * radius * radius
    println("Area of circle is $area")
}

Using kotlin.math.PI is more idiomatic and recommended over Math.PI.

Complexity: O(1) time, O(1) space

Time Complexity

The calculation uses a fixed number of operations regardless of input size, so it is O(1).

Space Complexity

Only a few variables are used, so space complexity is O(1).

Which Approach is Fastest?

All approaches perform the same constant-time calculation; using a function improves readability but does not affect speed.

Approach	Time	Space	Best For
Direct calculation	O(1)	O(1)	Simple quick calculation
Function method	O(1)	O(1)	Reusable and clear code
Using kotlin.math.PI	O(1)	O(1)	Idiomatic Kotlin code