c - Malloc works without type cast before malloc

I am learning about malloc function & I read
this:

ptr=
            malloc(sizeof(int)*N)

where
N is the number of ints you want to create. The only problem is what does ptr point at?
The compiler needs to know what the pointer points at so that it can do pointer
arithmetic correctly. In other words, the compiler can only interpret ptr++ or ptr=ptr+1
as an instruction to move on to the next int if it knows that the ptr is a pointer to an
int. This works as long as you define the ptr to be a pointer to the type of variable
that you want to work with. Unfortunately this raises the question of how malloc knows
what the type of the pointer variable is - unfortunately it
doesn't.

To solve this problem you can use a
TYPE cast. This C play on words is a mechanism to force a value to a specific type. All
you have to do is write the TYPE specifier in brackets before the value.
So:

ptr = (*int)
            malloc(sizeof(int)*N)

But
I have seen many places that they don't use (*int) before the malloc & even I made a
linked list with this and had no errors. Why is that?
Also, why do pointers
need to know anything except the size of memory they are pointing to?
But then
again I am quite new to this, so only the malloc doubt would do for
now.

Answer

Before you can use
ptr, you have to declare it, and how you declare it is the
pointer becomes.

malloc
returns void * that is implicitly converted to any
type.

So, if you have to declare it
like

int *ptr;
ptr =
            malloc(sizeof(int)*N);

ptr
will point to an integer array, and if you declare
like

char
            *ptr;

ptr =
            malloc(sizeof(char)*N);

ptr
will point to a char array, there is no need to
cast.

It is advised not to cast a return value
from malloc.

But I have seen
many places that they don't use (*int) before the
malloc & even I made a
linked list with this and had no errors. Why is


that?

Because they
(and you also surely) declared the variable previously as a pointer which stores the
return value from
malloc.

why do pointers need to know anything except the size of memory they

are pointing
to?

Because
pointers are also used in pointer arithmetic, and that depends on the type it is pointed
to.