increment and decrement without basic math operators

increment.c

#include<stdio.h>

int increment(int *c)
{
	int x=1;
	while((*c)&x)
	{
		*c^=x;
		x<<=1;
	}
	*c^=x;
	return *c;
}

int decrement(int *c)
{
	int x=1;
	while(!((*c)&x)&&x!=0)
	{
		*c^=x;
		x<<=1;
	}
	*c^=x;
	return *c;
}
int main()
{
	for(int i = -2;i<=16;)
		printf("%d\n",increment(&i));
	for(int i=16;i>=-2;)
		printf("%d\n",decrement(&i));
    return 0;
}