describe pointers and const's

main.c

#include <stdio.h>

int main()
{
    /*
     * int const p = 20; // p is a const int
     * printf("p = %d\n", p);
     */

    /*
     * const int pi = 20;
     * printf("pi = %d\n", pi);
     */

    /*
     * const int *p; // p is a pointer to int const, that is to say, *p is read-only
     * int const d = 300;
     * p = &d;
     * printf("int const @p = %d\n", *p);
     * int const f = 500;
     * // *p = f; //  read-only variable is not assignable
     */

    /*
     * int const *p; // p is a pointer to const int, that is to say, *p is read-only
     * const int d = 300;
     * p = &d;
     * printf("int const @p = %d\n", *p);
     * int const f = 500;
     * // *p = f; // read-only variable is not assignable
     */

    /*
     * int d = 300;
     * int *const p = &d; // p is a const pointer to int, that is to say, p is read-only but the value p points to is mutable
     * printf("int @p = %d\n", *p);
     * d = 500;
     * printf("int @p = %d\n", *p);
     * *p = 800;
     * printf("int @p = %d\n", *p);
     * printf("int d = %d\n", d);
     */

    /**
     * There is no const *int p;
     */

    /*
     * int const d = 300;
     * const int *const p = &d; // p is a const pointer to int const, that is to say, p and *p are both read-only
     * // p = &d; // cannot assign to variable 'p' with const-qualified type 'const int *const'
     * printf("int const @ const pointer p is %d\n", *p);
     */

    /*
     * const int d = 300;
     * int const *const p = &d; // p is a const pointer to const int
     * // p = &d; // cannot assign to variable 'p' with const-qualified type 'const int *const'
     * printf("const int @ const pointer p is %d\n", *p);
     */
}