pat 1001. A+B Format

#include<stdio.h>  int main()  {    int a,b;    int sum;    while(scanf("%d%d\n",&a,&b) != EOF){          sum = a+b;      if(sum < 0){      printf("-");      sum = -sum;      }      if(sum>=1000000){          printf("%d,%03d,%03d\n",sum/1000000, (sum/1000)%1000, sum%1000);      }      else if(sum >= 1000){          printf("%d,%03d\n",sum/1000,sum%1000);      } else{          printf("%d\n", sum);      }    }    return 0;  }