Why calloc? It zeros the memory and, as such, will touch every page allocated, forcing the kernel to actually create a physical page for it. This is wasteful, IMO, especially if you'll be writing to that memory again immediately (as he is) or, worse, if you'll be writing to the memory sparsely. Plus, I always thought that "calloc(x, y)" was pretty much equivalent to "malloc(x*y)" minus the obvious zeroing of the returned memory.
I've never seen a malloc implementation return int, but since the compiler assumes any functions that it hasn't seen a definition for take integer parms and return int, casting is a good way to step on your foot if you forget to include the header for malloc, lol. I've seen this before, and it's not pretty when someone spends forever trying to debug a core dump due to the compilers' (mis)understanding that malloc returns int and sign extends the result badly into the pointer causing its value to be incorrect and, thusly, causing a crash. All warnings were suppressed because of the cast. (BTW, it wasn't me, lol. I was the one who noticed stdlib wasn't included, and upon me were bestowed many thanks, lol). Of course, to this day I still have to force myself not to cast the result of malloc, but that day inspired me to stop doing it.