逆序遍历数组

for i in (0...10).reversed() {
    print(i)
}

// 3 ,2,1,0
for i in stride(from: 3, through: 0, by: -1) {
     print(i)
}

把字符或者字符串转成整型

func toNum(_ char: Character) -> Int {
    let intValue = Int(String(char))
    if let value = intValue {
        return value
    } else {
        return 0
    }
}