Control Flow and Loops

-- An 'if' decides which code runs based on a true/false test.
-- Shape:   if <condition> then ... elseif <condition> then ... else ... end
-- EVERY if block must be closed with the word 'end'.
local score = 85

if score >= 90 then
  print("Grade: A — Excellent!")     -- runs only when score >= 90
elseif score >= 80 then
  print("Grade: B — Great job!")     -- prints: Grade: B — Great job!
elseif score >= 70 then
  print("Grade: C — Good effort")
else
  print("Grade: F — Keep practising")
end

-- Note the single word 'elseif' — NOT 'else if' (that would need two 'end's).
-- Lua checks each test top to bottom and stops at the FIRST one that is true.

-- Relational operators compare two values and give back true or false.
print(5 == 5)      -- prints: true    (== means "equal to")
print(5 ~= 4)      -- prints: true    (~= means "NOT equal to")
print(5 ~= 5)      -- prints: false
print(7 > 3)       -- prints: true
print(7 >= 7)      -- prints: true
print(2 <= 1)      -- prints: false

-- IMPORTANT: Lua writes "not equal" as  ~=  (tilde-equals).
-- It is NOT  !=  — writing  5 != 4  is a SYNTAX ERROR in Lua.

-- == also compares strings character by character:
print("cat" == "cat")   -- prints: true
print("cat" == "Cat")   -- prints: false   (case-sensitive)

-- Logical operators in Lua are WORDS: and, or, not  (not && || !).
local age = 20
local hasID = true

print(age >= 18 and hasID)    -- prints: true    (both sides must be true)
print(age < 13 or age > 65)   -- prints: false   (needs at least one true)
print(not hasID)              -- prints: false   ('not' flips true/false)

-- Lua has NO ternary operator (no  cond ? a : b ).
-- The idiom is:  cond and a or b
local isAdmin = true
local role = isAdmin and "Admin" or "User"
print(role)                   -- prints: Admin

-- Read it as: if isAdmin is truthy, the result is "Admin", otherwise "User".
-- (One catch: it breaks if 'a' could itself be false or nil — rare for beginners.)

-- 1) NUMERIC for:  for var = start, stop[, step] do ... end
for i = 1, 5 do
  print(i)                 -- prints: 1, then 2, 3, 4, 5 (one per line)
end

-- A 3rd number is the STEP. Use a negative step to count down:
for i = 10, 1, -2 do
  print(i)                 -- prints: 10, 8, 6, 4, 2
end

-- 2) while: repeat the body WHILE a condition stays true.
-- Lua has no -- or -= shortcuts, so write 'fuel = fuel - 1' in full.
local fuel = 3
while fuel > 0 do
  print("Fuel:", fuel)     -- prints: Fuel: 3 / Fuel: 2 / Fuel: 1
  fuel = fuel - 1
end

-- 3) repeat ... until: like do-while — the body always runs AT LEAST once,
-- then the test is checked at the BOTTOM (loop ends when it becomes true).
local attempts = 0
repeat
  attempts = attempts + 1
until attempts >= 3
print("Tried", attempts, "times")   -- prints: Tried	3	times

-- The generic for walks over a table using an iterator function.

-- ipairs(t): array-style, integer keys 1,2,3... IN ORDER, stops at first gap.
local inventory = {"sword", "shield", "potion"}
for slot, item in ipairs(inventory) do
  print(slot, item)        -- prints: 1 sword / 2 shield / 3 potion
end

-- pairs(t): walks EVERY key, including string keys. Order is NOT guaranteed.
local player = { name = "Aria", level = 7, hp = 100 }
for key, value in pairs(player) do
  print(key, value)        -- prints each pair, e.g. name Aria / level 7 / hp 100
end

-- 'break' exits the nearest loop immediately:
for i = 1, 100 do
  if i > 3 then break end   -- stops the loop once i passes 3
  print(i)                  -- prints: 1, 2, 3
end

-- Lua has NO 'continue'. To skip an iteration, wrap the rest in an if:
for i = 1, 5 do
  if i % 2 == 0 then        -- only act on ODD numbers
    print(i, "is odd")      -- prints: 1 is odd / 3 is odd / 5 is odd
  end
end