Question

There is a piece of C code

int i, j = 0;
for (i = 0, j = n-1; i < n; j = i++) {
    // array operations
}

that I’m trying to convert into Lua code

local j = n-1
for i = 1, n do -- arrays are 1-based in Lua
    -- array operations
    j = i+1
end

but for some reason Lua code doesn’t work. Am I getting that C loop right?

Answer 1

Imagine an array as a circular buffer. i is the current item and j is always the previous one:

n = 5
local j = n
for i = 1, n do -- arrays are 1-based in Lua
    -- array operations
    io.write('i=', i, ' j=', j, '\n')
    j = i
end

Demo:

i=1 j=5
i=2 j=1
i=3 j=2
i=4 j=3
i=5 j=4