Swift Compiler Error Arithmetic operation '** ' (on type '**') results in an overflow (溢出运算符'&+')

Swift Compiler Error Arithmetic operation '****** ' (on type '****') results in an overflow

错误代码:

错误原因是数值运算中出现溢出情况.其结果超过了UInt8的0~255的范围. 和OC不同的是默认不允许在运算中数值溢出.但可以使用溢出运算符来运算