how Can I make a Sine Function in swift [closed] - swift

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I have tried the following but it gives me nan
func sin (x: Double) -> Void {
var z = 1000
var n = 1.0
var w = 0.0
var b = (2*n-1)+1
var c = 0.0
while (b > 2){
c *= (b-1)
b -= 1
}
while (z > 0){
w += (power(x:(-1), y:(n-1))*(power(x:x, y:(2*n-1)))/c)
z -= 1
n += 1
}
print(w)
} where
power(x:base, y: exponent)

Answer 1

Example:
func sin(_ x: Double) -> Double {
func factorial(_ number: Int) -> Int {
var result = 1
for i in 2...number {
result *= i
}
return result
}
let x2 = x * x
let x4 = x2 * x2
let t1 = x * (1.0 - x2 / Double(factorial(3)))
let x5 = x4 * x
let t2 = x5 * (1.0 - x2 / (6 * 7)) / Double(factorial(5))
let x9 = x5 * x4
let t3 = x9 * (1.0 - x2 / (10 * 11)) / Double(factorial(9))
let x13 = x9 * x4
let t4 = x13 * (1.0 - x2 / (14 * 15)) / Double(factorial(13))
let result = t1 + t2 + t3 + t4
return round(1000 * result) / 1000
}
Usage:
let test = sin(90 * Double.pi / 180) // 90 degrees
print(test) // 1.0

Answer 2

The bug is obviously the c = 0, which you then multiply with more and more numbers... That's one of the situations where you can say "I don't know what that code does, but it's wrong".
sin x = x - x^3 / 3! + x^5 / 5! - x^7 / 7! etc.
A not completely inefficient approach is to start with the term x, and then figuring out how you get from one term to the next. You don't add up 1000 terms, that's ridiculous. You add up terms until adding the next term doesn't change the sum anymore.
And when you have this working, print sin (0.1), sin (0.2), say to sin (100.) and tell us if you find something unusual.