Objective

The objective is to get the class to write a Go program to print strings to the terminal.

Creating this program will require the class to use the text editor (either Atom or LiteIDE) to create and save the source code file and the terminal/command line to run their program.

Why words second?

After numbers, words, or more correctly strings, are a fundamental concept in computing. Computers need strings. Without them how could any information be conveyed between the computer and the user.

Strings are used as a form of both output, to the screen and input, from the keyboard, to the computer program.

Learning outcome

The class should be able to:

  • Understand the relationship between characters and numbers
  • Understand what a string is
  • Start their text editor
  • Create a source code file
  • Write a simple program to print strings
  • Save a source code file
  • Build and run their program
  • Understand that the program represents a sequence
  • Understand that the sequence executes in order

Teaching prerequisites

The example program is sufficiently simple that the little or no additional teaching should be required beforehand. However the class needs to have covered

  • Basic keyboard/typing and mouse skills.
  • The latin alphabet

Sequences. The program demonstrates a sequence of instructions that are executed in order to print the results to the terminal window.

The is a direct link to English language, both in terms of the letters and pronunciation. There is also an indirect list to Foreign languages, though the use of different non-latin writing systems. This can be further linked to Geography.

Confusion between words and strings

We have used the term “word” initially because the class will be familiar with the concept as used in English. However we have introduced the correct term of “string” as soon as possible. You should therefore use the term string in your teaching. The term string is universal across all programming languages. The Go documentation refers strictly to stings and runes. As such the terms need introduced as early as possible.

Strictly a word in computer science is directly related to the hardware of the computer and specifically to the CPU. A word in this context is a fixed number of bits - now typically 32 or 64 bits. This is called the word size of the CPU. The word size is the number of bits that the CPU will process as a single block. The word size therefore matches the size, in bits, of the CPU’s general purpose registers.

CPU registers are small, but its faster to access memory elements within the CPU itself rather than in the computers main memory. The registers are where all of the CPU’s instructions are carried out. Data must therefore be loaded from main memory into the CPU registers, manipulated in the registers and stored back into main memory. This is the called LOAD/STORE architecture.

The word size also determines the maximum amount of memory that the CPU can physically access. A CPU with a 32 bit word size will have 32 so called address lines - these are physical wires on the circuit board - connecting the CPU to the memory. This limits the maximum about to memory to 232 bits or 4 gibibits (GiB).

What is a character?

Notes for slide 4

A computer can only process numbers. This restriction means that each letter must be mapped to a unique number. The Unicode standard provides that mapping, for every letter, symbol, and logograms, for every written human language.

Go uses the term rune to denote the unique number used to represent a single letter, symbol or logograms.

Unicode letter encoding

Notes for slide 5

The Unicode Table website can show you the whole Unicode set. Your class should be able to use this table to find the number that represents each number.

To find the number used for a letter you need to hover over the each letter in the table. The number used for the letter will then be displayed.

When using the table, the number along the horizontal and vertical access are displayed in hexadecimal i.e. base 16. Hovering over any symbol in the full table will display U+0041 | Dec: 65. The U+0041 is the standard way to write a unicode character, a capital U followed by a + followed by a number in hexadecimal that represents the position in the table. The second part, the Dec: 65 is the decimal equivalent of the hexadecimal number.

The number 65 represents the capital letter A.

The answers to the questions are:

A is 65

Z is 90

a is 97

b is 98

c is 99

d is 100

0 is 48

9 is 57

space is 32 - this is the blank tile to the left of ! in the table

+ is 43

$ is 36

Æ is 198

Ə is 399

ξ is 958

79 is the capital letter O

61 is an equals sign, =

55 is the number 7

101 is the lower case letter e

This mapping via the Unicode table from letters or symbols used in writing to a single unique number is an example of a character encoding. This is the key fact that the pupils must grasp. Letters are represented by numbers through an encoding.

Notes

You may see reference to other character encodings, notably ASCII, (American Standard Code for Information Interchange), or a CodePage 1252 Windows LATIN 1. These are alternative character encoding systems that have been superseded by Unicode. These alternative systems only supported the Latin alphabet and where limited to a maximum of 256 letters or symbols. Leaving non-Latin languages or languages with much larger alphabets to devise their own incompatible encodings. Unicode was created to unify this situation. The first 256 entries of the Unicode table match (more or less) the Latin characters as defined in the ASCII set.

A string is a Sequence of Characters

Notes for slide 6

A string is like a sentence in English. But, it can contain anything that can by typed at the keyboard. The string is not restricted to contain only letters and punctuation. The following are all valid strings.

Hello World!
L3tt3r5 and Numb3r5 can be M1x3d
You can type maths as well 1+1=2
Or you can have nonsense like this !"£$%^&*())*+}{~@:?><¬|}\"

Any sequence or any length you can type on a keyboard is s string.

Go has strict definition of a string. Go defines a string as a sequence or runes.

Strings in Go

Notes for slide 7

A string is Go must be typed inside inverted commas, one at each end of the string. Like this

"This is a string!"

The string must also be typed on one line. This string would be illegal.

"This is a string
is illegal because it is
typed one more than one line."

This is a pattern. All strings in Go must follow this pattern. If the string does not it is a syntax error.

To turn the lines

That wasn't flying. That was falling with style!
You are a sad, strange little man, and you have my pity.

into strings, you simply need to enclose them in inverted commas. Like this

"That wasn't flying. That was falling with style!"
"You are a sad, strange little man, and you have my pity."

The mistake in the example string

"To infinity... and beyond!

is a missing inverted commas at the end of the string. It is correctly written as

"To infinity... and beyond!"

Additional Class Exercise

Can the class identify which of these strings are correct? Can they find the mistakes?

"You know, that little droid is going to cause me a lot of trouble."

If you're saying that coming here was a bad idea, I'm starting to agree with
you."

"He is as clumsy as he is stupid!

"For over a thousand generations, the Jedi were the guardians of peace and
justice in the Old Republic - before the dark times. Before the Empire."

The first string

"You know, that little droid is going to cause me a lot of trouble."

is correct. There are inverted commas " at the start and end of the string.

The second string

If you're saying that coming here was a bad idea, I'm starting to agree with
you."

is wrong. There are inverted commas, " at the end of the string but the inverted commas, ", at the start of the string as missing. The string can contain commas and apostrophes.

The third string

"He is as clumsy as he is stupid!

is also wrong. The inverted commas, ", at the end of the string is missing.

The last one is tricky.

"For over a thousand generations, the Jedi were the guardians of peace and
justice in the Old Republic - before the dark times. Before the Empire."

The string is wrong because it is typed over two lines. Strings can only by typed in a single line.

How to Print a String

Notes for slide 8

Printing a string on the computers terminal window as output requires the use of one of two functions. The two functions are called Print and Println. The functions are part of the fmt package, sort for format.

The functions are used like this

fmt.Println("This is a string!")
fmt.Print("and so is this.")

These lines are called statements. Go programs consist of a sequence of statements. The statements are the Go instructions to the computer.

The string to be printed appears between the brackets, the ( and ). This string must be correct. You must also type everything one line. The line always starts with fmt.Print or fmt.Println. Notice that this is the package name, fmt followed by a period, followed by the function name. This is the pattern for printing to the screen.

We have not explained packages yet, so the pupils can consider the functions to be named fmt.Println and fmt.Print at this stage.

The fmt.Println and fmt.Print functions are not the same. The fmt.Print prints the string that you put in between the brackets. The next fmt.Print or fmt.Println function will continue to print on the same line. The fmt.Println function also prints the string that you put in between the brackets but also takes a new line at the end. The next string that you print with fmt.Println or fmt.Print will be on the next line.

If you had typed this into a program (ignore the line numbers, they are for illustration only)

    1 fmt.Println("Printed on Line 1")
    2 fmt.Print("Printed on Line 2")
    3 fmt.Println(" also printed on Line 2")
    4 fmt.Println("Printed on Line 3")

The output would be this

    1 Printed on Line 1
    2 Printed on Line 2 also printed on Line 2
    3 Printed on Line 3

The fmt.Print function does take a new line at the end, so lines 3 and 4 in the program produce line 3 in the output.

The string on slide 8

And there seems to be no sign of intelligent life anywhere.

Would be printed using fmt.Println and fmt.Print like this

fmt.Println("And there seems to be no sign of intelligent life anywhere.")
fmt.Print("And there seems to be no sign of intelligent life anywhere.")

The mistakes in the fmt.Println and fmt.Print statements

fmt.Println"Who invited that kid?")
fmt Print("So play nice!")

are. The first example is missing an opening bracket before the opening inverted comma. The second example is missing the period between fmt and Print. It has been replaced with a space. The correct statements would be

fmt.Println("Who invited that kid?")
fmt.Print("So play nice!")

Additional Class Exercise

Can the class spot which of these statements is wrong? Can they explain their answers?

fmt.Println "You are a member of the rebel alliance, and a traitor.")
fmt Print("Would it help if I got out and pushed?!!")
fmt.Println("Try not. Do… or do not. There is no try."
fmt.Println "What have you done?! I’m BACKWARDS."
fmt.Println("The circle is now complete."
fmt-Print("You’ll find I’m full of surprises!)
fmt.Println(We seem to be made to suffer. It’s our lot in life.)
fmt.Print("It’s against my programming to impersonate a deity.")

The first line is wrong.

fmt.Println "You are a member of the rebel alliance, and a traitor.")
It is missing the opening bracket, (.

The second line

fmt Print("Would it help if I got out and pushed?!!")
is also wrong. It is missing the full stop between fmt and Print. Instead it has a space.

The third line

fmt.Println("Try not. Do… or do not. There is no try."
is also wrong. The closing bracket, ), at the end of the line is missing.

The fourth line

fmt.Println "What have you done?! I’m BACKWARDS."
is also wrong. This line is missing both brackets, ().

The fifth line

fmt.Println"The circle is now complete.")
is also wrong. It is also missing the opening bracket, ( before the
double quote mark, &quot;

The sixth line has two mistakes

fmt-Print("You’ll find I’m full of surprises!)
The first mistake is that the full stop,. has been replaced by a minus sign, -, between the fmt and Print. The second mistake is the closing double quote, " is missing before the closing bracket, )

The seventh line also has two mistakes.

fmt.Println(We seem to be made to suffer. It’s our lot in life.)
This line is missing both the opening and closing double quote marks around the string. There should be a double quote mark after the opening bracket, ( and another one before the closing bracket, )

The last line

fmt.Print("It’s against my programming to impersonate a deity.")
is the only one that is correct. It has the full stop between fmt and Print, both brackets, ( and ) and the string is surrounded by double quote marks, ".

A string between " marks is called a interpreted string literal in Go.

Advanced Class Exercise

Ask the class to write down the output of these fmt.Println and fmt.Print statements.

fmt.Println("Ready are you? What know you of ready? For eight hundred years")
fmt.Print("have I trained Jedi. ")
fmt.Print("My own counsel will I keep on who is to be trained. ")
fmt.Println("A Jedi ")
fmt.Println("must have the deepest commitment,")
fmt.Print(" the most serious mind. ")
fmt.Print("This one, a long time")
fmt.Println(" have I watched. ")
fmt.Println("All his life has he looked")
fmt.Println("away… to the future, to the horizon. Never his mind on where he")
fmt.Println("was. …Hmm? On what he was doing.")

The stringfun example program

Notes for slides 9 and 10

Lets look at the stringfun.go program in more detail. Here it is again.

    1 package main
    2 
    3 import (
    4    "fmt"
    5 )
    6 
    7 func main() {
    8    fmt.Println("The stringfun program shows you how to use strings.")
    9    fmt.Println("")
   10    fmt.Println("An example of printing words with the Println function.")
   11    fmt.Println("These words appears on one line, with a new line at the end.")
   12    fmt.Println("These words appear on the next line because of the the new line.")
   13    fmt.Println("Both lines are printed using the Println fuunction.")
   14    fmt.Println("The Println function always take a new line at the end.")
   15    fmt.Println("")
   16 }
Fig-1. The stringfun.go code

You should largely be able to understand this program. The structure is identical to the numbers.go program introduced in the Numbers lesson and the Numbers teacher notes. The program uses the same Println function from the fmt or format package as was used previously to print to the screen. The only significant difference is that the strings printed by each of the Println functions is different, compared to the numbers.go program.

Lines 1 to Line 6 define the main package and imports the fmt package as before.

Line 7 is again the main function. The program begins execution here.

Lines 8 to line 15 are example uses of the fmt.Println function to print strings to the terminal. The fmt.Println statements all follow the same pattern.

The expected output of the program is

The stringfun program shows you how to use strings.

An example of printing words with the Println function.
These words appear on one line, with a new line at the end.
These words appear on the next line because of the new line.
Both lines are printed using the Println function.
The Println function always take a new line at the end.

Plenary

Notes for slide 11

Yes the string

"The word I’m searching for, I can’t say, because there’s preschool toys present."

is correct.

No, the fmt.Println statement

fmt Println "How did I get stuck with you as a moving buddy?)

is incorrect. The statement is missing a period between fmt and Println. The statement is missing the opening bracket, (. The statement is missing the closing inverted commas. The correct statement would be

fmt.Println("How did I get stuck with you as a moving buddy?")

fmt.Println prints a string and then prints a newline. Further output will appear on the new line.

The example string would be printed with a fmt.Println statement like this

fmt.Println("In a galaxy far far away...")

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