diagonal

diagon.cpp

#include <iostream>
#include <iomanip>
#include <vector>
#include <cmath>
#include <fstream>

using namespace std;

int main(int argc, char *argv[])
{
	int n;
	vector<int> m;
	ifstream file;
	file.open("i2", ifstream::in);
	if (!file.is_open()) {
		cerr << "error" << endl;
		return 1;
	}
	while (file) {
		file >> n;
		m.push_back(n);
	}
	int a = sqrt(m.size());
	for (int i = 0; i < a; i++) {
		for (int j = i; j < a; j++) {
			cout << setw(3) << m.at(i * a + j);
		}
		cout << endl;
	}
	file.close();
	return 0;
}