Calculate Pi

pi.swift

import Foundation

srand48(Int(arc4random()))

func rand(from: Double, to: Double) -> Double {
    assert(to - from > 0)
    let seed = drand48()
    return seed * (to - from) + from
}

/// The size of the rectangle
let a = 10.0

/// The radius of the inner circle
let r = a / 2

///
let loopCount = 100000000

var circleCount = 0

let rangeLower = -5.0
let rangeUpper = 5.0

for _ in 0..<loopCount {
    let x = rand(from: rangeLower, to: rangeUpper)
    let y = rand(from: rangeLower, to: rangeUpper)
    
    if x * x + y * y <= r * r {
        circleCount += 1
    }
}

let rate = Double(circleCount) / Double(loopCount)
let pi = (rate * a * a) / (r * r)
print(pi)