Lua by Example: For

for is one of Lua’s looping constructs. Here are some types of for loops.

A three expression loop is called a numeric for loop i=1 is the initial condition, 5 is the end condition, 1 is the step increment the third expression is optional, when omitted 1 is used as the step.

 
for i=1, 5, 1 do
    print('first: ', i)
end

Note the variable declared in the loop is local to the body of the loop despite the lack of the local keyword.

 
print('loop variable scope is local:', i) -- will print nil
 
print()

break can be used to end the loop early

 
for i=1, 10, 1 do
    print('brk: ', i)
    if i == 5 then
        break
    end
end
 
print()

A generic for loop supports traversing elements returned from an iterator print all values of array arr

 
arr = {'a', 'b', 'c', 'd'}
for i,v in ipairs(arr) do
    print('arr: i, v', i, v)
end
 
print()

Lua does not have a continue construct. A workaround is to use goto. This code prints odd numbers in the range [1,5] inclusive.

 
for i=1, 5 do
  if i % 2 == 0 then goto continue end
  print('odd: ', i)
  ::continue::
end
 
$ lua for.lua
first:     1
first:     2
first:     3
first:     4
first:     5
loop variable scope is local:    nil
 
brk:     1
brk:     2
brk:     3
brk:     4
brk:     5
 
arr: i, v    1    a
arr: i, v    2    b
arr: i, v    3    c
arr: i, v    4    d
 
odd:     1
odd:     3
odd:     5

Next example: While.

by Blake Bourque | source | license