1001 A+B Format

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 −10​6​​≤a,b≤10​6​​. 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

Analyse:

    First, we can calcuate a + b and obtain the result. The next step is to turn 'int' which is format of the result into 'string'. We can use ostringstream and istringstream to get what we want. Traverse every char in the string and add commas in appropriate positions.

    The reason why I write this blog is that I want to claim from today on I'll solve those problems which belong to PAT advanced level. I wish I can write blogs in English.

#include<iostream>
#include<sstream>

using namespace std;

int main(){
	int a, b;
	string result;
	cin >> a >> b;
	a = a + b;
	ostringstream os;
	os << a;
	istringstream is(os.str());
	is >> result;
	if(result[0] == '-'){
		cout << '-';
		result.erase(0, 1);
	}
	//add commas 
	for(int i = result.length() - 1, j = 1; i >= 0; i--, j++){
		if(j % 3 == 0 && i != 0){
			result.insert(i, 1, ',');
		}
	}
	cout << result;
	return 0;
}