K4 is the implementation language of q, kdb is the database part of the language. Most q is just named utility functions written in K4. There isn't really much difference in what the machine does with them under the covers, but when stuck on a problem talking about q is more likely to get help than k.

You can provide up to 8 named inputs in a function definition.

q example for running sum of 8 inputs:

  q)f:{[a;b;c;d;e;f;g;h]sums a,b,c,d,e,f,g,h}

same in K4:

  q)\
  f:{[a;b;c;d;e;f;g;h]+\a,b,c,d,e,f,g,h}

The default variable names go all the way up to z. So you I would write your function as:

    f:{z+y*x}

(k is evaluated strictly right to left - another design decision that I quite like -, so I had to move the variables around in the expression)

If you wish, you can provide your own variable names as follows:

    f:{[a;b;c]c+b*a}

This works in k and q (q is largely k with some nice-to-have functions defined on top).