how const works

foo.c

#include <stdio.h>

int main(int argc, char *argv[])
{
	char a, b;
	char const * s;
	char * const p;

	s = &a;
	p = &b;

	*s = '-';
	*p = '-';

	return 0;
}

gistfile1.txt

foo.c: In function ‘main’:
foo.c:10:2: error: assignment of read-only variable ‘p’
  p = &b;
  ^
foo.c:12:2: error: assignment of read-only location ‘*s’
  *s = '-';
  ^