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 −106≤a,b≤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
题目分析：
计算两个整数的和，并且这两个整数范围很正常，不大于10^6，
有一点需要注意的是输出需要用题目要求的格式（每3位用逗号分割），可以使用字符串转换把a，b的和转换成字符串，然后对字符串进行操作。
#include<iostream> #include<string> 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; }
关键语句：
if ((i + 1) % 3 == len % 3 && i != len - 1)
i != len - 1 很好理解，就是对最后一位的判断。
((i + 1) % 3 == len % 3 就是在找逗号的位置，i从0开始，所以i+1，因为输出是从前往后输出，索引要用 len%3 找逗号的位置。
比如12,345 ； 12，345，678
