PAT甲级——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)

Sample Input:

-1000000 9
Sample Output:
-999,991

第一种方法，注意题目说明的数字范围，及时处理越界即可。
为啥捏，因为 int 是32位的，最大2的31次方。题目给的数据容易越界

第二种方法，使用to_string将A+B的值转化为字符串，按需要的格式进行修改。
string s = to_string(a + b);
to_string的用法推荐查阅官方文档，表述清晰

string to_string (int val);
string to_string (long val);
string to_string (long long val);
string to_string (unsigned val);
string to_string (unsigned long val);
string to_string (unsigned long long val);
string to_string (float val);
string to_string (double val);
string to_string (long double val);

Convert numerical value to string
Returns a string with the representation of val.

第二种方法较为简单清晰。

#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;
}