What You are Going to Learn?

In the last lesson we showed you how to use numbers in your programs. Now we want to talk about letters and words.

Strings not words

In computer science the term word relates to the CPU . A word is the number of bits that the CPU can process in a single operation.

A word like a word or a sentence in English is called a string in programming.

You use strings to print words letters, numbers and symbols to the screen. A string contains the data that the computer should print to the screen. It does not tell the computer what size to print strings or which font to use.

What is a Character?

Before we talk about stings we have to talk about characters. Characters are the letters, numbers, punctuation and mathematical symbols on your keyboard that a computer can print to the screen.

Each character is represented by a number in a table. Each character in the table has a unique number. The numbers are assigned by the Unicode standards committee.

The Unicode table website contains the complete table. Open the table in you web browser.

Notes

The table is very large so it may be slow to load.

If you find the capital letter A and hover over it with your mouse you will see U+0041 | Dec: 65. The important part is Dec: 65 which tells you that the capital letter A is number 65 in the table. A capital letter B is 66. A number 1 is at number 49. An explanation mark, !, is at number 33 in the table. A space is one before at number 32.

Now it is your turn

Using the Unicode table, can you find the numbers that are used to represent these letters?

X

Y

z

4

&

?

X is the number 88

Y is the number 89

z is the number 122

4 is the number 52

& is the number 38

? is the number 63

So when you type a letter A the computer knows you really mean number 65. If you remember that computers can only process numbers. This is why we have to convert what you see as a letter to a number. This is called an encoding. The letters are encoded or represented by numbers.

You might be wondering why this table is so large. It is because the table has to work for all of the world’s languages.

The Chinese language has around 3500 characters, actually called logograms, in common use but has as ,many as 109,000 in total. These are all in the table. To make these easy to find you need to group the table by “block”. Once you do that you need to find the block called “CJK Unified Ideographs” to see just some of them.

The Japanese alphabet appears twice, once for each of the two native Japanese writing systems of Hiragana and Katakana.

There is also the Arabic, Hebrew and Russian alphabets along with many more as well as all of the mathematical symbols.

Now it is your turn

Using the Unicode table can you find the numbers that are used to represent these letters from other languages?

Ŋ

Ɣ

ɸ

Ŋ is number 331

Ɣ is number 194

ɸ is number 632

So a character might not be an English letter as you think of it. A character could also be an logogram or a mathematical symbol.

To make things clear, Go uses the term rune to represent any of the letters, Iogograms and symbols in the Unicode table. Rune is the term used in the Go documentation. This means that in Go a string is defined as a sequence of runes not characters.

What is a String?

By now you might be asking just what is a string? A string is a sequence of characters. The characters are strung together. This is why we call them strings.

Unlike in English, a string can contain letters, numbers, spaces, and punctuation. As string can contain any sequence of any length that can be typed on a keyboard.

These are all valid strings

Bananaman and Danger Mouse
Numb3r5 and l3tt3r5
1+1 equals two
nonsense line this $)djkasdkjjadai)($£())
you@your.email.address.com

How to use strings in Go

If you have already tried the Numbers you have already been using stings!

The simplest way is to create a string use inverted commas, ", like this:

"This is a string!"

This is the approach you have seen before. Do you notice that there is a pattern? You must use inverted commas, " at the start and the end of the string.

Strings also have to be typed on one line. This string is illegal because it is typed across more than one line

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

This is another pattern. The string must be typed on one line. These two patterns are some of the syntax rules of Go. If a string does not follow this pattern there is a syntax error.

Now it is your turn

Now you know what a string should look like, which of these strings are correct? Can you work 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 double quotes marks " 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 is missing. The string can contain commas and apostrophes.

The third string

"He is as clumsy as he is stupid!

is also wrong. The double quote mark, ", 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

You can print a string on the computers terminal window using two functions. The two functions are called fmt.Print and fmt.Println.

You use the functions like this

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

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

You need to tell both functions the string you want to print. Can you see the pattern for this?

You have to type your string between the brackets, the ( and ). You must also type everything on one line. The line always starts with fmt.Print or fmt.Println. This is the pattern for printing to the screen.

Now it is your turn

Now can you spot which of these lines is wrong? Can you explain your 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, "

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 inverted commas 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, ".

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 ( and ). The fmt.Println function also prints the string that you put in between the brackets, the ( and ) 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

    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

Notes

Ignore the line numbers in both the program and the output. We have added them so we can talk about specific lines in the program.

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.

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

Now it is your turn

What should these lines print out?

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 program

Let’s write a Go program to put all of this string knowledge into practice. Just as we did with the numbers program are going to put this program in its own directory.

First open your Terminal program or Command Prompt. In your terminal you need to change to the location of your Go Workspace. To do this you need to type

On Linux, Raspberry Pi and Mac OS X

cd $GOPATH/src/

On Windows

cd %GOPATH%\src\

Now you need to make a new directory. We need to call this stringfun after the program we will write. Then we need to change directory into the new stringfun directory.

mkdir stringfun
cd stringfun

Now you need to start you editor, either Atom or LiteIDE

On Linux, Windows and MacOS X

atom stringfun.go

On Raspberry Pi

liteide stringfun.go
    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 function.")
   14    fmt.Println("The Println function always take a new line at the end.")
   15    fmt.Println("")
   16 }
Fig-1. The stringfun.go code

Once you have typed the program in, you need to save it. Once you have saved it you need to run it with:

go run stringfun.go

If you typed the program correctly you should see

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.

Let’s look at the important parts of the program. First is line 8.

fmt.Println("The stringfun program shows you how to use strings.")

Line 8 prints the message

The stringfun program shows you how to use strings.

to the screen. You can see that the line follows the pattern for printing to the screen. It starts with fmt.Println and has and opening bracket, ( and a closing bracket ). The string that is printed is enclosed in inverted commas, ".

We have used the fmt.Println function here, so the output of the next fmt.Println or fmt.Print line will appear on the next line

Lines 10, 11, 12, 13 and 14 are similar. These lines print different strings to the screen but the pattern is the same.

Next lets look at line 9.

fmt.Println("")

You know that whatever you type between the inverted commas in printed out to the terminal by the Println function followed by a new line. But what happens here?

Look at what the program printed to the terminal when you ran it. This is the output of the program. If you look at the second line you can see that nothing is printed. It is an empty line. Now look at the string in line 9; there is nothing between the inverted commas. This is called an empty string. The string exists but there are no runes in it to print out. When you print an empty string nothing happens. There is no output.

But why is there an empty line? If you remember that the Println always takes a new line after it has printed out a string. In this case it prints an empty string before it takes a new line. The result is shown in the output. The whole line is empty and the output is a blank line. Output will continue on the line after the blank line.

If you want to print a blank line, this is the pattern you must use. You have to use two fmt.Println functions one after the other. The first fmt.Println function should print the string you want, the second fmt.Println function should print an empty string. This combination prints the blank line in the output.

You can see that we have printed another blank lines at lines 15. Notice the fmt.Println on line 14.

Now it is your turn

Now it is your turn to write a program to use strings.

You need to edit, the stringfun.go program so that the computer prints out some new strings. Once you have changed the program, you will need to run it again to make sure that it worked.

Important

Before you run your program you must save your file again. If you do not, you will run the same version of the program as before, so you will not see the effect of your changes.

If you want to save your new program under a new name you can. But you can’t have any spaces in the new name and it still has to have a .go file extension. If you do this you will need to remember the new name because you will need that to run your program. For example. If you called your new program extra-strings.go then you would run it like this

go run extra-strings.go

Change your program so that it prints this message at the end

Somewhere in that pad of stuffing is a toy who taught me that life's only worth
living if you're being loved by a kid. And I traveled all this way to rescue
that toy, because I believed him.

You need to use fmt.Println functions to print each of the lines in the output.

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