【PAT甲级】 A+B Format（字符串size的类型为unsigned 整数）

本文介绍了一种计算两个整数之和并将结果以标准格式输出的方法，具体包括读取输入、计算总和及将结果转换为带有逗号分隔符的字符串格式。示例代码使用了C++，并考虑了正负数的情况。

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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

思路：

字符串的size()返回值为 unsigned int类型，因此在用其做判断时要注意强制转化 int 型.

CODE：

#include<iostream>
#include<string>
using namespace std;
typedef long long ll;
int main() {
	ll a, b;
	while (cin>>a>>b)
	{
		ll c;
		c = a + b;
		char d = ' ';
		string temp = to_string(c);
		if (temp[0] == '+' || temp[0] == '-') d = temp[0], temp = temp.substr(1);

		int i = 0;
		while ((int)temp.size() - 3 * (i + 1) - i>0)
		{
			
			temp.insert(temp.size() - 3 * (i + 1)- i,",");
			i++;
		}
		d == ' ' ? cout << temp << endl : cout << d << temp << endl;
	}

}