Chapter 3: Making Decisions

Your game has been saying "the door is locked" since chapter 2, but it's been lying. Nothing has actually checked whether it should be locked. Every program you've written so far runs the same way no matter what the player does. That changes now.

The if Statement

if lets your program choose whether to run a block of statements at all.

var hasKey = false

if hasKey then
    writeln("You unlock the door and step inside.")
end if

Run that with hasKey set to false, and nothing happens, the block between if and end if is skipped entirely. Set it to true, and the line runs. if always needs a matching end if to mark where its block stops.

Comparison Operators

Most conditions come from comparing two values:

==   // equal to
!=   // not equal to
<    // less than
>    // greater than
<=   // less than or equal to
>=   // greater than or equal to

var age = 12

if age >= 13 then
    writeln("You may enter the tavern.")
end if

A few rules worth knowing before they surprise you. First, == compares strings case-sensitively, "Key" and "key" are not equal. Second, <, >, <=, and >= require both sides to be the same type, you can compare two numbers or two strings, but comparing a number to a string directly is an error, not an automatic conversion. If you ever need to compare a number the player typed in against a string, convert it first with num(), the same way you did back in chapter 2.

Else and Else If

if on its own only handles one path. else gives you a fallback, and else if lets you check additional conditions in order.

if hasKey then
    writeln("You unlock the door and step inside.")
else if knowsPassword then
    writeln("You whisper the password. The door creaks open.")
else
    writeln("The door stays shut.")
end if

QF Code checks each condition top to bottom and runs only the first branch that matches. Once one branch runs, the rest are skipped, even if they would also have been true.

Combining Conditions

and, or, xor, and not let you build a single condition out of several smaller ones.

if hasKey and knowsPassword then
    writeln("Overkill, but the door opens immediately.")
end if

if hasKey or knowsPassword then
    writeln("One is enough. The door opens.")
end if

if not hasKey then
    writeln("You'll need to find a key.")
end if

and and or short-circuit, meaning and stops checking as soon as one side is false, and or stops as soon as one side is true. xor is different: it always checks both sides, and it's true only when exactly one of them is.

One thing to unlearn if you've dabbled in other languages before: QF Code won't let you treat a string or a number like 5 as a stand-in for true or false. Logical operators only accept actual booleans, or the numbers 0 and 1. Anything else, a string, an array, empty, raises an error rather than quietly guessing what you meant.

Growing the Adventure

Time to make the door actually respond to the player.

// The Hollow Cottage
// Chapter 3

const cottageName = "The Hollow Cottage"

writeln("You are standing outside " + cottageName + ".")

var playerName = input("What is your name, traveler? ")
writeln("Welcome, " + playerName + ".")

var answer = input("There is a riddle carved into the door. It asks: what has keys but no locks? ")

if answer == "piano" then
    writeln("The door swings open. You step inside.")
else
    writeln("Nothing happens. The door stays shut.")
end if

Run it, answer correctly, answer wrong, watch both paths actually behave differently. That's the whole idea of this chapter, made real.

Make It Yours. Write your own riddle, or replace it with a password, a choice between two doors, or anything else where the player's answer should change what happens next. Give it at least one else or else if branch, not just a single if.

// The Hollow Cottage
// Chapter 3

const cottageName = "The Hollow Cottage"

writeln("You are standing outside " + cottageName + ".")

var playerName = input("What is your name, traveler? ")
writeln("Welcome, " + playerName + ".")

var answer = input("There is a riddle carved into the door. It asks: what has keys but no locks? ")

if answer == "piano" then
    writeln("The door swings open. You step inside.")
else
    writeln("Nothing happens. The door stays shut.")
end if