Draw Pascal's triangle with simple format

pascal_triangle.cc

#include <bits/stdc++.h>
using namespace std;

void pascals_triangle(int n)
{
    n = 1 << (n+1);
    vector<vector<bool>> a;
    a.resize(n);
    a[0].resize(1);
    a[0][0] = 1;
    for (int i = 1; i < n; ++i) {
        a[i].resize(i+1);
        a[i][0] = a[i][i] = 1;
        for (int j = 1; j <= i-1; ++j) {
            a[i][j] = a[i-1][j-1] ^ a[i-1][j];
        }
    }
    for (int i = 0; i < n; ++i) {
        for (int x = 0; x < n-1-i; ++x) {
            cout << ' ';
        }
        for (int j = 0; j <= i; ++j) {
            cout << (a[i][j] ? 'O' : '.');
            if (j < i) cout << ' ';
        }
        cout << endl;
    }
}

int main()
{
    pascals_triangle(3);
}