（甲）1001. A+B Format

题目：http://www.patest.cn/contests/pat-a-practise/1001

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

分析：加法谁都会做，关键是格式化输出。我这里把负数转成正数再弄。应该会有更好的办法，

using namespace std;
void formatOutput(int n);
int main()
{
int a, b;
cin >> a >> b;
formatOutput(a + b);
return 0;
}
void formatOutput(int n)
{
if (n == 0)
{
cout << '0' << endl;
return;
}
if (n < 0)
{
cout << '-';
n = -n;
}
int bit = 1,i=0;
for (; n / bit; i++) bit*=10;
bit /= 10;
for (int j = i; j >0; j--)
{
if (j != i && j % 3==0)
cout << ',';
cout << n/bit;
n -= ((n / bit)*bit);
bit /= 10;
}
cout << endl;
}