Question 1 :
malloc() returns a float pointer if memory is allocated for storing float's and a double pointer if memory is allocated for storing double's.
Question 2 :
malloc() allocates memory from the heap and not from the stack.
Question 3 :
malloc() returns a NULL if it fails to allocate the requested memory.
Question 4 :
If malloc() successfully allocates memory it returns the number of bytes it has allocated.
Syntax: void *malloc(size_t size);
The malloc() function shall allocate unused space for an object whose size in bytes is specified by size and whose value is unspecified.
The order and contiguity of storage allocated by successive calls to malloc() is unspecified. The pointer returned if the allocation succeeds shall be suitably aligned so that it may be assigned to a pointer to any type of object and then used to access such an object in the space allocated (until the space is explicitly freed or reallocated). Each such allocation shall yield a pointer to an object disjoint from any other object. The pointer returned points to the start (lowest byte address) of the allocated space. If the space cannot be allocated, a null pointer shall be returned. If the size of the space requested is 0, the behavior is implementation-defined: the value returned shall be either a null pointer or a unique pointer.