PAT 1001. A+B Format (20)

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

Each input file contains one test case. Each case contains a pair of integers a and b where -1000000 <= a, b <= 1000000. The numbers are separated by a space.

Output

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：先存储两数的相加结果，判断正负，负输出‘-’，然后把结果转化为正数统一运算。在这里有三种可能，结果小于1000直接输出，结果介于1000和1000000之间的，中间要有‘，’隔开，这可以用取余和除于1000来分别输出逗号两边的数，类似的最后一种情况也这样做。
 
#include <cstdio>

int main()
{
	int a, b, c;
	while (scanf("%d %d", &a, &b) != EOF)
	{
		c = a + b;
		if (c < 0) {   //先输出负数符号，把负数转换为正数，方便下面输出
			printf("-");
			c = -c;
		}
		if (c <1000)
			printf("%d\n", c);
		else if (c < 1000000)
		        printf("%d,%03d\n", c/1000, c%1000);
		     else
		        printf("%d,%03d,%03d\n",c/1000000, (c % 1000000) / 1000, c%1000 );
	}
	return 0;
}