More Words and strings

What You are Going to Learn?

In the last lesson you learned what a string was and the pattern that all strings must follow in Go.

In this lesson you are going to practice fixing some mistakes in programs that use strings. You will also learn an approach to fixing syntax errors.

What is a String?

Each letter, number or symbol on the keyboard is called a character. A string is a sequence of these letters, numbers or symbols. Anything that can by typed on a keyboard is considered a string.

Each character in every human language has a unique number. The number is defined by the Unicode character encoding. The computer can only process numbers so it works with these unique numbers, and not with the letters or symbols themselves. This means that a string is also a sequence of numbers.

Because the concept of a character is different for different languages, for example Chinese uses logograms, Go uses the term rune instead of character.

A string in Go is therefore a sequence of runes.

The Pattern to Create a String in Go

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

"Strings, I see you now"

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

"A horse, a horse,
my kingdom for a horse"

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 line

I have been chosen! Farewell, my friends. I go on to a better place.

into a string, you need to surround it in inverted commas. Like this

"I have been chosen! Farewell, my friends. I go on to a better place."

I don't believe that man's
ever been to medical school!"

"I don't believe that man's ever been to medical school!"

The Pattern to Print a String in Go

Printing a string requires the use of one of two functions. The two functions are called fmt.Print and fmt.Println. Printing to the screen is a type of output.

The functions are used like this

fmt.Println("First string")
fmt.Print("and second string.")

These lines are called statements.

The pattern to print to the screen is this. The statement always starts with fmt.Print or fmt.Println. The upper case letters are important, so the spelling must be exactly as shown. There must be a full stop between the fmt and the Println or Print. The string you want to print is in between the brackets, the ( and ).

Remember, 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 printed on the next line.

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

1Printed on Line 1
2Printed on Line 2 and also printed on Line 2")
3Printed on Line 3

Syntax Errors

If a fmt.Println or fmt.Print statement does not follow the correct pattern there is an error. This is called a syntax error. Go will not run a program that contains any syntax errors. Your program must be free of syntax errors first.

Following this pattern is like following the correct spelling in English writing. If the spelling is wrong the writing will not make sense.

Here are couple of ways to find syntax errors.

• The programmer looks closely at the program and finds then. This is ultimately what is required. You will become better at spotting and correcting these mistakes with practice.
• The programmer can notice that the syntax highlighting in their editor is not correct. This is an attempt by the editor to show the programmer that there is likely a syntax error.
• Code review - the programmer asks a friend to review his source code. A fresh pair of eyes is often a valuable tool itself!
• The programmer can also try to run the program. In this case Go will find the syntax errors for the programmer and report the line with the syntax error. This approach is a double edged sword. It is very effective, but there can be many error reports. The first syntax error will often cause further lines in the program to contain syntax errors. We are going to show you an example of this in a minute.

Fixing a syntax error is much simpler than finding it. The line in the source code file that contains the error must be found and edited to remove the error. The source code file then needs saving again. Another attempt to run the program can now be made. If no more syntax errors exist the program will run. Otherwise you have to repeat the process with the next error.

The badstring program

This is the badstring.go program. The program contains syntax errors and will not run until these are fixed.

 1package main
 2
 3import (
 4	"fmt"
 5)
 6
 7func main() {
 8    fmt.Println("Lightning McQueen: I'm a very famous race car!")
 9    fmt.Println "Luigi: You are famous race car? A real race car?")
10    fmt.Print("Lightning McQueen: Yes, I'm a real race car, ")
11    fmt.Println(what do you think? Look at me.")
12    fmt.PRINTLN("Luigi: I have followed racing my entire life, my whole life")
13    fmt.Println(Lightning McQueen: Then you know who I am. I am Lightning McQueen.)
14    FMT.Println("Luigi: Lightning McQueen!")
15    fmt.Println("Lightning McQueen: Yes! Yes!)
16    fmt.Print(Luigi: I must scream it to the world, my excitement from the ")
17    fmt.Println("top of someplace very high. Do you know many Ferraris?")
18    fmt.Print("Lightning McQueen: No, no, no, they race on the European circuit; ")
19    fmt.Println("I'm in the Piston cup.")
20    fmt.Println"Lightning McQueen: What?"
21    Println("Luigi: Luigi follow only the Ferraris.")
22}

What would Go do?

But what would Go do if we tried to run the badstring without correcting the errors? Lets find out.

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

cd $GOPATH/src/

cd %GOPATH%\src\

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

mkdir badstring
cd badstring

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

atom badstring.go

liteide badstring.go

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 badstring.go

When you attempt to run the program you should see this.

./badstring.go:9: syntax error: unexpected string literal, expecting semicolon or newline or }
./badstring.go:11: syntax error: unexpected name, expecting )
./badstring.go:11: syntax error: unexpected ?
./badstring.go:11: newline in string
./badstring.go:13: syntax error: unexpected name, expecting )
./badstring.go:15: newline in string
./badstring.go:16: syntax error: unexpected name, expecting )
./badstring.go:16: newline in string
./badstring.go:20: syntax error: unexpected string literal, expecting semicolon or newline or }

filename:line number:error message

If you look at the error messages it correctly tells you that line 9 has a syntax error. However if you look at the error message it does not make the error immediately obvious. Neither is the solution obvious.

Also notice that the errors snowball. There errors on line 9, 11, 13, 15, 16 and 20 are found, but the ones on lines 12, 14, and 21 are masked by the earlier errors.

This output is typical of a program that contains syntax errors.

How does Anyone Solve this?

First don’t panic! You can learn how to use this output to help you find the errors. You just need to take three steps.

The first step is to learn the patterns. The error messages tell you where you might have an error. We say might because this where Go detected the error. The cause may be several lines before.

The second part is to be systematic and logical. The computer is not wrong, there is a reason for the error somewhere in the program. Your task is to find it and correct the mistake. You need to look very carefully at the line. A single character added, missed or a small letter when you wanted a capital letter is sufficient to trigger a syntax error. You use the patterns to find these mistakes.

The last part is to work in stages. You should try to solve one error at a time. Start at the fist error and attempt to fix that. When you make a change that you think fixes the mistake, save the program, and try to run the program again. If you have fixed the error then there should be one less the number of errors in the output. You know the error has been fixed. Then you have to tackle the next error using the same approach.

The corrected badstring program

This is the corrected badstringprogram.

 1package main
 2
 3import (
 4	"fmt"
 5)
 6
 7func main() {
 8	fmt.Println("Lightning McQueen: I'm a very famous race car!")
 9	fmt.Println("Luigi: You are famous race car? A real race car?")
10	fmt.Print("Lightning McQueen: Yes, I'm a real race car, ")
11	fmt.Println("what do you think? Look at me.")
12	fmt.Println("Luigi: I have followed racing my entire life, my whole life")
13	fmt.Println("Lightning McQueen: Then you know who I am. I am Lightning McQueen.")
14	fmt.Println("Luigi: Lightning McQueen!")
15	fmt.Println("Lightning McQueen: Yes! Yes!")
16	fmt.Print("Luigi: I must scream it to the world, my excitement from the ")
17	fmt.Println("top of someplace very high. Do you know many Ferraris?")
18	fmt.Print("Lightning McQueen: No, no, no, they race on the European circuit; ")
19	fmt.Println("I'm in the Piston cup.")
20	fmt.Println("Lightning McQueen: What?")
21	fmt.Println("Luigi: Luigi follow only the Ferraris.")
22}

The output of the program is

Lightning McQueen: I'm a very famous race car!
Luigi: You are famous race car? A real race car?
Lightning McQueen: Yes, I'm a real race car, what do you think? Look at me.
Luigi: I have followed racing my entire life, my whole life
Lightning McQueen: Then you know who I am. I am Lightning McQueen.
Luigi: Lightning McQueen!
Lightning McQueen: Yes! Yes!
Luigi: I must scream it to the world, my excitement from the top of someplace very high. Do you know many Ferraris?
Lightning McQueen: No, no, no, they race on the European circuit; I'm in the Piston cup.
Lightning McQueen: What?
Luigi: Luigi follow only the Ferraris.

The Programming Challenge

Now you know enough about strings to make your own changes. Are you ready for your challenge?

Lightning McQueen: Okay, here we go. Focus. Speed. I
am speed. One winner, forty-two losers. I eat losers
for breakfast. Breakfast? Maybe I should have had
breakfast? Brekkie could be good for me. No, no, no,
focus. Speed. Faster than fast, quicker than quick. I
am Lightning.