//input contains hexidecimal number
char hex;

sscanf(input, "%x", &hex);
//...

twos_compliment = -number;

int main()
{
	int		number;
	int		two;

	number = 100;
	two = ~number;		//One's compliment
	two = two + 1;		//Two's compliment

	printf("Original number is: %d(%x)\n",number,number);
	printf("Two's compliment is: %d(%x)\n",two,two);
	printf("Unsiged is: %u\n",two);
	printf("Negative number is: %d(%x)\n",-number,-number);

	return 0;

}

void convert(short bin, char *str)
{
    unsigned short mask;      // used to check each individual bit, unsigned
                            //    to alleviate sign extension problems

    mask = 0x8000;      // Set only the high-end bit
    while (mask)            // Loop until MASK is empty
    {
        if (bin & mask)     // test the masked bit
              *str = '1';   // if true, value is 1
          else
              *str = '0';   // if false, value is 0
        str++;              // next character
        mask >>= 1;         // shift the mask 1 bit
    }
    *str = 0;               // add the trailing null
}


int main()
{
	short		number;
	short		two;
	char		binary[20];

	number = 336;
	two = ~number;		//One's compliment
	two = two + 1;		//Two's compliment

	printf("Original number is: %hd(%hx)\n",number,number);
	printf("Two's compliment is: %hd(%hx)\n",two,two);
	printf("Unsiged is: %hu\n",two);
	printf("Negative number is: %hd(%hx)\n",-number,-number);

	convert(number,binary);
	printf("Number in binary is: %s\n",binary);

	convert(two,binary);
	printf("Number in binary is: %s\n",binary);

	return 0;

}