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 − 1 0 6 10^6 106 ≤a,b≤ 1 0 6 10^6 106 . 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
解题思路：
把a+b的和转为字符串s。除了第一位是负号的情况，只要当前位的下标i满足(i + 1) % 3 == len % 3并且i不是最后一位，就在逐位输出的时候在该位输出后的后面加上一个逗号。
解题代码：
#include <iostream>
using namespace std;
int main() {
int a, b;
cin >> a >> b;
string s = to_string(a+b);
int len = s.length();
for (int i=0; i<len; i++) {
cout << s[i];
if (s[i]=='-') continue;
if ((i+1)%3 == len%3 && i!=len-1) cout << ",";
}
return 0;
}