Why do strings work, but character and int arrays do not work in a pointer array?

Question

I understand if I add the arrays, st and st2, to give it space in the memory, and then add it to the pointer array, it shouldn't be a problem:

/* works */
int st[] = {0,31,28,31,30,31,30,31,31,30,31,30,31};
int st2[]= {0,31,29,31,30,31,30,31,31,30,31,30,31};
int *day_tab[]= {
        st,
        st2
};

But without first giving it space in memory, why do strings specifically work? The code below gives an error:

int *day_tab[]= {
        {0,31,28,31,30,31,30,31,31,30,31,30,31},
        {0,31,29,31,30,31,30,31,31,30,31,30,31}
};

so does the code below:

char *day_tab[]= {
        {'0','1','\0'},
        {'0','1','\0'}
};

but the code below works

char *day_tab[]= {
        "01",
        "01"
};

Answer 1

This

int st[] = {0,31,28,31,30,31,30,31,31,30,31,30,31};
int st2[]= {0,31,29,31,30,31,30,31,31,30,31,30,31};
int *day_tab[]= {
        st,
        st2
};

Is three arrays: two of integers (with their own storage), and one array of two elements which are pointers to the first two arrays.

However, this is not valid:

int *day_tab[]= {
        {0,31,28,31,30,31,30,31,31,30,31,30,31},
        {0,31,29,31,30,31,30,31,31,30,31,30,31}
};

As before you have declared an array of pointers to integers, but pointers to what? Those braced lists are not storage locations, they cannot be pointed to.

Your final example is basically valid but dangerous:

char *day_tab[]= {
        "01",
        "01"
};

It is an array of two pointers to characters, and those pointers are initialized with string literals. String literals are very special in that they are actually stored somewhere, usually in read-only memory, and they can be shared (so the "01" string used twice can be stored just once). Braced lists don't have this feature in C, it's only for string literals.

The reason the final code is dangerous is that it is char* not const char*. The non-const type is accepted for reasons of backward compatibility but is not a good idea because modifying the data in a literal string is not allowed. So you're setting yourself up for a potential disaster if you actually use those pointers to write to the "01" string storage.