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
结尾无空行
Sample Output:
-999,991

#include<cstdio>
int main()
{
	int a,b,sum;
	scanf("%d%d",&a,&b);
	sum=a+b;
	int out[7]; 
	if(sum<0)
	{
		printf("-");
		sum=-sum;
	}
	int len=0;
	do{
		out[len++]=sum%10;
		sum=sum/10;
	}while(sum!=0);
	for(int i=len-1;i>=0;i--)
    {
        printf("%d",out[i]);
		if(i%3==0&&i>0)
		printf(",");
		
	}
	return 0;
 }