// This code assumes an int is 32 bits for simplicity.
// In real code you might want to check sizeof(int)
// and adjust the mask and shift values unless you know
// it will only be run on machines with 32 bit ints.
int main()
{
	// Initial values
	// These can be read from a file or the command line or whatever :)
	int numerator = 13;
	int denominator = 45;

	// Store the fraction
	// First we mask (bitwise AND) with 0xFFFF (16 bits of all 1's, half of a 32-bit int)
	// to make sure the inputted numbers aren't bigger than 16 bits.
	// Then we shift the numerator 16 bits to the left
	// and bitwise OR it with the denominator.
	// numerator is now in the upper half of fraction,
	// and denominator is in the lower half.
	int fraction = ((numerator & 0xFFFF) << 16) | (denominator & 0xFFFF);


	// Retrieve the fraction parts
	// For n we use a bitmask to get only the upper half,
	// and then shift it back 16 bits to the right.
	// For d we just grab the lower half directly.
	int n = (fraction & 0xFFFF0000) >> 16;
	int d = fraction & 0x0000FFFF;

	printf("numerator = %d\n", n);
	printf("denominator = %d\n", d);
}

#define MAKEFRACTION(num,den)  (((num & 0xFFFF)<<16) | (den & 0xFFFF))
#define LOWPART(f)  (f & 0xFFFF)
#define HIGHPART(f) ((f>>16)&0xFFFF)

fraction = MAKEFRACTION(numerator,denominator);
numerator = HIGHPART(fraction);
denominator = LOWPART(fraction);