Binary representation of negative integer

Language : C++ 

/****************
Convert any -ve integer to binary
return int
if the number 0101 (which represents +5) is stored in a 4-bit word, its extension to an
8-bit word would be 0000 0101. Conversely, the extension of the 4-bit number 1101 (representing -3) to
an 8-bit word results in 1111 1101. This method ensures that the signed values remain unchanged after the
extension.
****************/
#include <iostream>
#include <climits>
unsigned long long int toBinary(int n) {
	if (n >= 0) {
		std::cout << "Sorry, wrong input" << std::endl;	
		return 0;
	}
	int m = ~n; //1's complement of n ... introduced to execute right shift
	unsigned long long int num = 0;
	unsigned long long int pow10 = 1;
	while (m) {
		num = (!(m & 1) * pow10) + num;
		m >>= 1;
		if (pow10 > ULLONG_MAX / 10 && m) {
			std::cout << "Sorry, storage issue" << std::endl;
			return 0;
		}
		pow10 *= 10;
	}
	num = pow10 + num;
	return num;	
}
int main() {
	int n;
	std::cout << "Enter a negative integer: ";
	std::cin >> n;
	if (!(toBinary(n)));
	else {
		printf("%32llu\n", toBinary(n));
		printf("Replace space padding with 1 :)\n");
	}
	std::cin.get();
}