problem

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

• 将两个数字相加，用标准格式输出最终结果

solution

• 两数相加开始还以为是高精度有点烦，结果1e6的数据怎么加都不会超过int的。
• 标准格式输出，想用string流但是不会（而且慢），想用除法和取模发现循环顺序不对，最后用了递归。（分三步优化）
• 提交WA了第四个点，考虑特殊数据 0 0时没有输出

#include<iostream>
using namespace std;
void output(int c, int cnt){
  if(!c)return ;
  if(cnt%3==0 && c/10!=0){
    output(c/10,cnt+1);
    cout<<",";
  }else output(c/10,cnt+1);
  cout<<c%10;
}
int main(){
  int a, b;
  cin>>a>>b;
  int c = a+b;
  if(c==0){
    cout<<0<<endl;
    return 0;
  }
  if(c<0){
    cout<<"-";
    c = -c;
  }
  output(c,1);
  return 0;
}