How to use function as a placeholder for codes

Question

I want to use function as a placeholder for a bunch of codes while making the function also produce an output

Consider

A={0,0,0};
f[x_]:=Block[{},A[[x]]=1;A]
f[1]

this will make A to be {1,0,0} while outputting A. (The Block[] is necessary. I don't know why, but it isn't my main question). My main question is how to make the following code work

f[A1_] := Block[{}, A1[[1]] = 1; A1]
A={0,0,0};
f[A]

I want this changes A to {1,0,0} while outputting it. How can i make this work? Are there alternatives for placeholder of codes? If my question shows an obvious lack on knowledge on some area, such as how defining function works, some reference would be helpful.

Answer 1

Give f the Attribute HoldFirst:

ClearAll[f]
f[A1_] := (A1[[1]] = 1; A1)

SetAttributes[f, HoldFirst]

A = {0, 0, 0};
f[A]

{1, 0, 0}