Constant Pointer Error in C

Question

//ok
int a=5;
int* const ptr=&a;

printf("%d ", *ptr);

//Error
int* const ptr2;
int b=56;

ptr2= &b;

printf("%d ", *ptr2);

Why the second part produces error as the output?

Answer 1

ptr2 is an undefined constant that cannot be changed.

Debug:
int* ptr2;
int b = 56;
ptr2 = &b;
printf(%d", *ptr2);