Cast

Part of the Fundamentals section of Coddy's Lua journey — lesson 32 of 90.

To convert the input to a different type, we need to cast.

To cast a string to a number, we will write:

var = io.read()
var = tonumber(var)

Or in one line,

var = tonumber(io.read())

If the input is a number, i.e. 5, 4, 54 then var will hold a number. If the input contains an invalid number: 5ab, bb, akt, etc. then tonumber() will return nil.

Here is a table that shows how to cast to different types:

Cast	Explanation
tonumber()	Convert to a number
tostring()	Convert to a string

It is important to use the right type because it can affect the output.

Concatenating two strings will result in:
"5" .. "5" = "55"

Adding two numbers will result in:
5 + 5 = 10

Challenge

Beginner

In this challenge, you'll work with multiple inputs and perform calculations.

How to receive multiple inputs:

var1 = io.read()  -- First input
var2 = io.read()  -- Second input

Your task:

Read the first number from input and store it in a variable
Read the second number from input and store it in another variable
Convert both variables to number type (for numeric calculations)
Calculate the multiplication of these two numbers
Print the result

Example:

If the inputs are 2 and 4.5, your program should output 9.0

Remember: Each test case contains exactly two inputs, one after the other.

Cheat sheet

Casting in Lua:

-- Convert string to number
var = tonumber(io.read())

-- Convert to string
var = tostring(io.read())

-- tonumber returns nil for invalid input
var = tonumber("abc")  -- var is nil

Important: Concatenating strings joins them, while adding numbers performs arithmetic:

"5" .. "5" = "55"  -- String concatenation
5 + 5 = 10          -- Numeric addition

Multiple inputs:

var1 = io.read()
var2 = io.read()

Try it yourself

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Fundamentals

1Introduction

The Language Hello World!Comments

4Operators 2 Relational & Logic

Equality Operators Relational Operators The 'and' Operator The 'or' Operator The 'not' Operator Short-Circuit Evaluation Truthy and Falsy Values Recap - Simple Logic

7Basic Conditional Logic

The if-then Statement The if-then-else Statement The elseif Statement Recap - Treasure Chest

10Tables Part 1: List-Style

What is a Table?Creating a Table Accessing Elements by Index Modifying Elements by Index The Length Operator '#'table.insert()table.remove()Recap - Manage Party Members

13Project: Simple Potion Shop

Project Setup Adding a Potion

Displaying the Inventory

Calculating Total Stock Value

Finding a Specific Potion

Selling a Potion

3Operators 1 Arithmetic & Conc

Arithmetic Operators Modulo Operator Exponentiation Operator String Concatenation Operator Precedence Recap - Simple Calculations

6Project: Character Stats Disp

Welcome Message Declare Character Stats

Display Basic Stats

Add a Boolean Flag

Final Summary

9Functions Basics

Declaring a Function Calling a Function Functions with Parameters Functions with Multiple Params The 'return' Statement Recap - Area Calculator

12Loops Basics

The while Loop The repeat-until Loop The Numeric for Loop for Loop with a Step The 'break' Statement Recap - Countdown

15Final Challenges

Recap - Player Turn Recap - Simple Database Recap - Sum of Even Numbers