Demo of std::vector with Collatz sequence

#include <iterator>
#include <vector>
using   std::size,      // From <iterator>
        std::vector;    // From <vector>

template< class Collection >
auto int_size( const Collection& c )
    -> int
{ return static_cast<int>( size( c ) ); }

auto is_even( const int v )
    -> bool
{ return v % 2 == 0; }

auto next_collatz( const int v )
    -> int
{ return is_even( v )? v/2 : 3*v + 1; }

auto collatz( const int n )
    -> vector<int>
{
    vector<int> result;
    for( int x = n; x != 1; x = next_collatz( x ) ) {
        result.push_back( x );
    }
    result.push_back( 1 );
    return result;
}

#include <iostream>
using std::cout, std::endl;     // From <iostream>

auto main() -> int
{
    const int n = 42;
    const vector<int> numbers = collatz( n );

    cout << "Collatz sequence starting with " << n << ", one per line:" << endl;
    cout << endl;
    for( const int v: numbers ) {
        cout << "> " << v << endl;
    }

    cout << endl;
    cout << "The same numbers but with all on one line:" << endl;
    cout << endl;
    cout << "> ";
    for( int i = 0; i < int_size( numbers ); ++i ) {
        if( i > 0 ) {
            cout << ", ";
        }
        cout << numbers[i];
    }
    cout << "." << endl;
}