For loops LUA Different Types

I wanted to learn more about for loops, as far as I know there are different types?

For instance,

for i = 1, 5 do
    print("hello")
end

^ I know about this one, it's going to print hello 5 times, but there are others like the one below which I do not understand, specifically the index bit (does that mean it is number 1?) and what is the ipairs for

for index, 5 in ipairs(x) do
    print("hello")
end

If there are any other types please let me know, I want to learn all of them and if you can provide any further reading I'd be more than greatful to check them out

Solution

As you can read in the Lua reference manual 3.3.5 For Statement

The for statement has two forms: one numerical and one generic.

The numerical for loop repeats a block of code while a control variable runs through an arithmetic progression. It has the following syntax:

stat ::= for Name ‘=’ exp ‘,’ exp [‘,’ exp] do block end

Example:

for i = 1, 3 do
  print(i)
end

Will output

1    
2    
3

You seem familiar with that one. Read the reference manual section for more details.

The generic for statement works over functions, called iterators. On each iteration, the iterator function is called to produce a new value, stopping when this new value is nil. The generic for loop has the following syntax:

stat ::= for namelist in explist do block end namelist ::= Name {‘,’ Name}

Example:

local myTable = {"a", "b", "c"}
for i, v in ipairs(myTable) do
  print(i, v)
end

Will ouput

1  a
2  b
3  c

ipairs is one of those iterator functions mentioned:

Returns three values (an iterator function, the table t, and 0) so that the construction

for i,v in ipairs(t) do body end will iterate over the key–value pairs (1,t[1]), (2,t[2]), ..., up to the first nil value.