Conditional statements allow your program to make decisions based on certain conditions. In Lua, you use if, elseif, and else to implement conditional logic.

The if statement evaluates a condition and executes a block of code if the condition is true. Code Example:

local devLevel = 18

if devLevel >= 18 then
    print("WOW! REALLY GREAT")
end

Explanation:

• if devLevel >= 18 then: This line checks if the variable age is greater than or equal to 18.
• print(“WOW! REALLY GREAT”): If the condition (devLevel >= 18) is true, then this line will execute and print “WOW! REALLY GREAT”

You can use elseif to check additional conditions and else to provide a default action if none of the conditions are true.

Code Example:

local temperature = 25

if temperature > 30 then
    print("It's hot outside!")
elseif temperature > 20 then
    print("It's warm outside.")
else
    print("It's cool outside.")
end

Exercise:

• Write an if statement to check if a variable number is positive.
• Extend the if statement with elseif and else to cover different ranges of values.
• Modify the variables and test different conditions to see the output.

Example Exercise Code:

local number = 10
 
if number > 0 then
    print("The number is positive.")
elseif number < 0 then
    print("The number is negative.")
else
    print("The number is zero.")
end

Loops are used to repeat a block of code multiple times. Lua supports while, for, and repeat…until loops.

The while loop repeats a block of code while a condition is true.

Code Example:

local i = 1
while i <= 5 do
    print("i = " .. i)
    i = i + 1
end

Explanation:

• local i = 1: Initializes a variable i with a value of 1.
• while i ⇐ 5 do: This line sets up the condition to execute the loop as long as i is less than or equal to 5.
• print(“i = ” .. i): Prints the current value of i.
• i = i + 1: Increments i by 1 in each iteration to avoid an infinite loop.

The for loop iterates over a range of values specified by the user.

Code Example:

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

Explanation:

• for i = 1, 5 do: This line initializes i to 1 and iterates up to 5.
• print(“i = ” .. i): Prints the current value of i in each iteration.

The repeat…until loop executes a block of code at least once and continues to repeat until a condition becomes true.

Code Example:

local i = 1
repeat
    print("i = " .. i)
    i = i + 1
until i > 5

Explanation:

• repeat: Starts the loop block.
• print(“i = ” .. i): Prints the current value of i.
• i = i + 1: Increments i by 1 in each iteration.
• until i > 5: Ends the loop when i becomes greater than 5.

Exercise:

• Write a while loop to count from 10 to 1 and print each number.
• Use a for loop to print even numbers from 1 to 10.
• Implement a repeat…until loop to prompt the user for input until they enter a valid number.

Example Exercise Code:

  -- while loop
  local countdown = 10
  while countdown >= 1 do
      print(countdown)
      countdown = countdown - 1
  end
 
-- for loop
for i = 2, 10, 2 do
    print(i)
end
 
-- repeat...until loop
local userInput
repeat
    print("Enter a number: ")
    userInput = io.read("*n")  -- Read a number from input
until userInput ~= nil
print("You entered: " .. userInput)

Functions are blocks of code that perform a specific task and can be reused throughout your program. They help in organizing code and making it more readable.

You define a function in Lua using the function keyword followed by the function name and parameters.

Code Example:

-- Function to calculate the square of a number
function square(num)
    return num * num
end
 
-- Calling the function
local result = square(5)
print("Square: " .. result)  -- prints: 25

Explanation:

• function square(num): Defines a function named square that takes a parameter num.
• return num * num: Computes the square of num and returns the result to the caller.

Functions can have parameters (input values) and return values (output values).

Code Example:

-- Function with parameters and return value
function greet(name)
    return "Hello, " .. name .. "!"
end
 
-- Calling the function
local message = greet("Lua Learner")
print(message)  -- prints: Hello, Lua Learner!

Exercise:

• Write a function that calculates the area of a rectangle given its length and width.
• Create a function that converts Celsius to Fahrenheit.
• Implement a function that checks if a number is prime and returns true or false.

Example Exercise Code:

-- Function to calculate the area of a rectangle
function calculateArea(length, width)
    return length * width
end
 
-- Function to convert Celsius to Fahrenheit
function celsiusToFahrenheit(celsius)
    return celsius * 9 / 5 + 32
end
 
-- Function to check if a number is prime
function isPrime(number)
    if number <= 1 then
        return false
    elseif number == 2 then
        return true
    else
        for i = 2, math.sqrt(number) do
            if number % i == 0 then
                return false
            end
        end
        return true
    end
end
 
-- Example usage
local area = calculateArea(5, 10)
print("Area of rectangle: " .. area)
 
local fahrenheitTemp = celsiusToFahrenheit(25)
print("Temperature in Fahrenheit: " .. fahrenheitTemp)
 
local num = 17
if isPrime(num) then
    print(num .. " is a prime number.")
else
    print(num .. " is not a prime number.")
end