Constant pointer to non-constant data

techdemo.c

#include <stdio.h>
int main(void) {
  int x = 8; // define x
  int y; // define y
  // constant location (pointer) to non-constant data
  int* const ptr = &x;
  // an attempt to modifiy the data will succeed
  *ptr = 55;
  printf("%d\n", x);
  // an attempt to modify the memory location will fail
  ptr = &y; /*error: assignment of read-only variable 'ptr'*/
}