【PAT甲级A1001 】A+B Format (20分)（c++）
1001 A+B Format (20分)作者：CHEN, Yue单位：浙江大学代码长度限制：16 KB时间限制：400 ms内存限制：64 MBCalculate a+b and output the sum in standard format – that is, the digits must be separated into groups of three by commas (unless there are less than four digits).Input Specif
