1001. A+B Format-PAT甲级

题目：

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 Each input file contains one test case. Each case contains a pair of integers a and b where -1000000 <= a, b <= 1000000. The numbers are separated by a space.

Output 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

翻译：

计算a + b并以标准格式输出，数字每三个分成一组（除非有少于四个数字）。

思路：

先计算a+b。 把得到的数字变成字符串。 每隔三个输出“，”号。

解答：

#include <string> #include <iostream> using namespace std; int main() { int a, b; cin >> a >> b; string s = to_string(a + b); int len = s.length(); int c = len % 3; for (int i = 0; i < len; i++) { cout << s[i]; if (s[i] == '-') continue;//第一次提交没有写这行代码，出现错误，还是要细心啊 if ((i + 1) % 3 == c && i != len - 1) cout << ","; } return 0; }

得到：

学会灵活运用to_string用法。在条件后加上“&& i != len - 1”来取消循环输出带来的输出错误。多设置变量保存数值，来减少运算次数及时间。