Code Puzzles

[davisdude]

I can't claim the last puzzle as mine- it's an Euler project puzzle.

[NickRock]

Try this without using a third variable to swap the numbers

Code: Select all

local a = 10
local b = 15

swap(a,b)
--[[
	Output:
	Current value of a is 15
	Current value of b is 10
]]

[bartbes]

You're probably going for the usual trick of a = a + b, b = a - b, a = a - b, but since lua has no call-by-reference semantics no such function can actually exist. (At least not without going into the debug library.)

[zorg]

You're probably going for the usual trick of a = a + b, b = a - b, a = a - b, but since lua has no call-by-reference semantics no such function can actually exist. (At least not without going into the debug library.)

So, you're saying that

Code: Select all

function swap(a,b) a, b = b, a end

won't work?

Edit: Ah, i see the real problem; yeah, would work with returning them.

Edit2: After the answer being posted, i realized that defining the function in that chunk means that the function can access the two vars as upvalues, if one doesn't pass them in as arguments. (The answer though is wrong, since they are being passed in, and the printing happens -inside- the function; it would fail (as in, give the wrong answer) if it was called outside, after calling swap.

[undef]

You're probably going for the usual trick of a = a + b, b = a - b, a = a - b, but since lua has no call-by-reference semantics no such function can actually exist. (At least not without going into the debug library.)

So, you're saying that

Code: Select all

function swap(a,b) a, b = b, a end

won't work?

No, but this will:

Code: Select all

function swap(a,b) _G.a, _G.b = b, a end

Edit:

No it won't, because the variables are local.

[zorg]

No, but this will:

Code: Select all

function swap(a,b) _G.a, _G.b = b, a end

Except a and b are locals, not globals, so sadly that won't work either. The debug library could probably get the two upvalues and then it might be possible though, as bartbes said before.

[undef]

Yep, just noticed that too... Debug libary then.

[NickRock]

I just did this

Code: Select all

function swap(a, b)
	a = a + b
	b = a - b
	a = a - b
	
	print("Current value of a is " .. a .. "\nCurrent value of b is " .. b)
end

and worked perfectly fine

[Ranguna259]

I just did this

Code: Select all

function swap(a, b)
	a = a + b
	b = a - b
	a = a - b
	
	print("Current value of a is " .. a .. "\nCurrent value of b is " .. b)
end

and worked perfectly fine

Why did you give the answer

I can't claim the last puzzle as mine- it's an Euler project puzzle.

I think you need to give use more information about the problem, I bet this was not presented like this in the euler project.

[NickRock]

Why did you give the answer

Ah damn I'm sorry, I just wanted to make sure that I didn't make any mistakes explaining the puzzle