//1
let optionalArray = [1, nil, 2, 3 , nil, 5]

var testNumber = 0

for number in optionalArray {
    testNumber += number ?? 0
}
print(testNumber)

//2
//======================================

let homeString = "123456789"
var inverseString = ""
var index = homeString.count - 1

while index >= 0 {
    inverseString.append(Array(homeString)[index])
    index -= 1
}
print(inverseString)