W1201 Scope

Within these castle walls be forged Mavens of Computer Science ...

— Merlin, The Coder

Prerequisites

• W1102 Type Overview

Research

• Read Scope (Wikipedia)
• Read Computer Science I Textbook (by Bourke) Chapter 2.2.4. Scoping

Experiment

Create a directory within your "project" directory.

cd ~/projects
mkdir project-1201
cd project-1201

Edit a new file named "main.swift"

emacs main.swift

For this project you'll repeatedly edit the same file. It's probably easiest to test this file within emacs by typing: M-& (async-shell-command) and observing the results. For each question, be sure to understand the behavior before proceeding to the next question. It will be helpful to record your answers and reasoning for later review.

Helpful hint: The async-shell-command can be executed with Alt-Shift-7. The command to execute each time is: swift main.swift

1

let x = 10
print(x)

What is output? (Ignore whitespace)

	21
	23
	10
	Compile or runtime error

2

let x = 10
print(x)
print(y)

What is output? (Ignore whitespace)

	21 23
	10 21
	Compile or runtime error
	10 10

3

let x = 10
print(x)
let x = 21
print(x)

What is output? (Ignore whitespace)

	Compile or runtime error
	21 23
	10 10
	10 21

4

let x = 10
print(x)
var x = 21
print(x)

What is output? (Ignore whitespace)

	Compile or runtime error
	10 21
	10 10
	21 23

5

let x = 10
print(x)
do {
    let x = 21
    print(x)
} //

	21 21
	10 10
	10 21
	Compile or runtime error

6

let x = 10
print(x)
do {
    let x = 21
    print(x)
} //
print(x)

	10 21 10
	Compile or runtime error
	10 21 21
	10 10 10

7

let x = 10
print(x)
repeat {
    let x = 21
    print(x)
} while x == 21
print(x)

	10 21 21
	Compile or runtime error
	10 21 10
	Infinite loop

8

let x = 10
print(x)
while x == 21 {
    let x = 21
    print(x)
} //
print(x)

	Compile or runtime error
	10 10
	10 21 10
	Infinite loop

9

let x = 10
print(x)
for x in 11 ... 11 {
    print(x)
    let x = x + 10
    print(x)
} //
print(x)

	10 10 20 10
	Infinite loop
	10 11 21 10
	Compile or runtime error

10

let x = 10
print(x)
for x in 11 ... 11 {
    print(x)
    x = x + 10
    print(x)
} //
print(x)

	Infinite loop
	Compile or runtime error
	10 11 21 10
	10 10 20 10