#include <iostream>
#include <stdlib.h>
#include <limits.h>

int find_significant_bits( long long n )
{
        if ( n < 0 ) 
                n = -n;
        unsigned max_bit_pos = 0;
        // find the position of the left-most bit that has the value `1':
        for ( unsigned i = 0; i < sizeof( long long ) * CHAR_BIT; ++i ) {
                if ( n & ( 1LL << i ) )
                        max_bit_pos = i;
        }
        // We are dealing with signed numbers,
        // so we need one more bit for the sign
        ++max_bit_pos;
        if ( max_bit_pos < CHAR_BIT )
                return CHAR_BIT;
        else if ( max_bit_pos < sizeof( short ) * CHAR_BIT )
                return sizeof( short ) * CHAR_BIT;
        else if ( max_bit_pos < sizeof( int ) * CHAR_BIT )
                return sizeof( int ) * CHAR_BIT;
        else if ( max_bit_pos < sizeof( long ) * CHAR_BIT )
                return sizeof( long ) * CHAR_BIT;
        else
                return sizeof( long long ) * CHAR_BIT;
}

void print_binary( long long n, int nbits )
{
        for ( int i = nbits - 1; i >= 0; --i ) {
                if ( i && i < nbits - 1 && ( i + 1 ) % 4 == 0 )
                        std::cout << ' ';
                if ( n & ( 1LL << i ) )
                        std::cout << 1;
                else
                        std::cout << 0;
        }
        std::cout << " (bin) \n";
}

int main( void )
{
        long long num;
        int bits_to_use;
        std::cout << "Enter a positive or negative number: ";
        if ( ! ( std::cin >> num ) ) {
                std::cerr << "Unable to read a number; giving up\n";
                exit( 1 );
        }
        bits_to_use = find_significant_bits( num );
        std::cout << num << " (dec) = ";
        print_binary( num, bits_to_use );
        std::cout << num << " == " << std::hex << std::showbase << num
                  << std::dec << '\n';
        return 0;
}