CODEWITHSUNDEEP
lua
prapin
prapin

Reputation: 6898

Incrementation in Lua

I am playing a little bit with Lua.

I came across the following code snippet that have an unexpected behavior:

a = 3;
b = 5;
c = a-- * b++; // some computation
print(a, b, c);

Lua runs the program without any error but does not print 2 6 15 as expected. Why ?

Upvotes: 35

Views: 63933

Answers (8)

Foggzie
Foggzie

Reputation: 9821

Lua doesn't increment and decrement with ++ and --. -- will instead start a comment.

Upvotes: 18

xo1337
xo1337

Reputation: 1

You can do the following:

local default = 0
local max = 100

while default < max do
     default = default + 1
     print(default)
end

Upvotes: -2

TERIHAX
TERIHAX

Reputation: 255

There are 2 problems in your Lua code:

a = 3;
b = 5;
c = a-- * b++; // some computation
print(a, b, c);

One, Lua does not currently support incrementation. A way to do this is:

c = a - 1 * b + 1
print(a, b, c)

Two, -- in Lua is a comment, so using a-- just translates to a, and the comment is * b++; // some computation.

Three, // does not work in Lua, use -- for comments.

Also it's optional to use ; at the end of every line.

Upvotes: 0

Werner Bessinger
Werner Bessinger

Reputation: 31

EDIT: Using SharpLua in C# incrementing/decrementing in lua can be done in shorthand like so:

a+=1 --increment by some value
a-=1 --decrement by some value

In addition, multiplication/division can be done like so:

a*=2 --multiply by some value
a/=2 --divide by some value

The same method can be used if adding, subtracting, multiplying or dividing one variable by another, like so:

a+=b
a-=b
a/=b
a*=b

This is much simpler and tidier and I think a lot less complicated, but not everybody will share my view.

Hope this helps!

Upvotes: -2

user4700203
user4700203

Reputation:

This will give 

3 5 3

because the 3rd line will be evaluated as c = a.

Why? Because in Lua, comments starts with --. Therefore, c = a-- * b++; // some computation is evaluated as two parts:

  1. expression: c = a
  2. comment: * b++; //// some computation

Upvotes: 3

Seniru Pasan
Seniru Pasan

Reputation: 801

There isn't and -- and ++ in lua. so you have to use a = a + 1 or a = a -1 or something like that

Upvotes: 14

user6697869
user6697869

Reputation:

If you want 2 6 15 as the output, try this code:

a = 3
b = 5
c = a * b
a = a - 1
b = b + 1
print(a, b, c)

Upvotes: 4

Esailija
Esailija

Reputation: 140234

-- starts a single line comment, like # or // in other languages.

So it's equivalent to:

a = 3;
b = 5;
c = a

Upvotes: 40

Related Questions