pointer_weird.c

#include <stdlib.h>
#include <stdio.h>
int main (int argc, char** argv) {
	int *x = (int*)malloc(sizeof(int));
	*x = 3;
	int *y = x;
	printf("x: %d, y:%d\n",*x,*y);
	free(x);
	printf("x: %d, y:%d\n",*x,*y);
	free(y);
}
// Or did you mean
#include <stdlib.h>
#include <stdio.h>
int main (int argc, char** argv) {
	int *x = (int*)malloc(sizeof(int));
	*x = 3;
	int **y = (int**)malloc(sizeof(int*));
	*y = x;
	printf("x: %d, y:%d\n",*x,*(*y));
	free(x);
	printf("x: %d, y:%d\n",*x,*(*y));
	free(y);
}

In the first case you don't have to free y (it causes a double free) because y = x; in the second case, y is allocated (to hold a pointer to int) and so must be freed. Hence no error in the second one.