Converting An Int To Little-endian Byte Array?

I'm converting a stream of bytes from a network packet into a specific struct, and vice versa. For example, when converting a short back and forth, my method looks like this:

myShort = buf(0) + (buf(1) * 256)
or the other direction:
buf(0) = myShort mod 256
buf(1) = myShort 256

When it comes to a 4 byte integer, after some experimentation I found that converting from the byte array to integer is done this way:

myInt = buf(0) + (buf(1) * 256) + buf(2) + (buf(3) * 256)

Basically adding two shorts together. I'm not quite sure to do the reverse of that, to fill the 4 bytes from myInt.