Is Valid Number

//no exponent
//6.  or .4 are valid
// only + or - are not valid
// +. are not valid
import Foundation

func validDouble(_ s:String) -> Bool{
    guard s.count > 0 else { return false }
    let arr = Array(s.trimmingCharacters(in: .whitespaces))

    var foundDot = false
    var i = 0
    var hasValue = false
    while i < arr.count {
        let char = arr[i]
        if i == 0 && (char == "+" || char == "-"){
            i += 1
            continue
        }
        if char == "." {
            if foundDot { return false}
            foundDot = true
            i += 1
            continue
        }
        if char < "0" || char > "9" { return false}
        hasValue = true
        i += 1
    }
    return hasValue
}