Your question really is the following. If I've written something in the functional programming paradigm, how do I port it to a language in the imperative programming paradigm? The only real answer is that you have to be a good programmer with both paradigms and think about how'd you implement the corresponding code. C doesn't have anonymous functions, so you can't have an equivalent of Slot.
Here's an example piece of functional code in Mathematica:
Map[ #^2+1&, {1,2,3,4,5}]
Here is the equivalent imperative code in Mathematica
f[x_]:= x^2+1
vector = {1, 2, 3, 4, 5};
accumulator = {0, 0, 0, 0, 0};
For[i = 1, i <= Length@vector, i++, accumulator[[i]] = f[vector[[i]]]]
The imperative code is what you'd be able to easily port to C.
Of course, you can always use a different datastructure than an array to hold the output, which is here called accumulator.
As a side note, you can sorta do functional programming in C with function pointers, which would allow you to write something like Map above, but that'd be up to you do decide if you wanted to get involved in that mess.
