#include <iostream>
#include <iostream>
#include <vector>
#include <cstdlib>
#include <ctime>

int main()
{
	std::size_t n ;
	std::cout << "Enter the size of matrix:\n";
	std::cin >> n ;
    std::vector< std::vector<int> > a( n, std::vector<int>(n) ) ;

    std::srand( std::time(nullptr) ) ;
    for( std::size_t i = 0 ; i < n ; ++i )
    {
        a[i][i] = 1 ; // diagonal
        for( std::size_t j = i+1 ; j < n ; ++j )
            a[i][j] = a[j][i] = std::rand() % 10 ;
    }

    for( const auto& row : a )
    {
        for( int v : row ) std::cout << v << ' ' ;
        std::cout << '\n' ;
    }
}