PAT-A 1001 A+B Format （20 分）

1001 A+B Format （20 分）

Calculate 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 Specification:

Each input file contains one test case. Each case contains a pair of integers a and b where −10​6​​≤a,b≤10​6​​. The numbers are separated by a space.

Output Specification:

For each test case, you should output the sum of a and b in one line. The sum must be written in the standard format.

Sample Input:

-1000000 9

Sample Output:

-999,991

思路：

1.使用int保存计算中的数字，不会溢出。

2.如果和的结果数字部分不够4位，直接输出。

3.否则，使用sprintf将和保存到字符数组中，根据正负打印数字和逗号即可。