More Variables more practice

What You are Going to Learn?

You are going to practice declaring and assigning values to variables in this lesson. This will help you learn the patterns for variable declaration and variable assignment.

Declaring a Variable

To declare or create a variable you need three pieces of information. They are

• The var keyword that is used to introduce a variable.
• The variable name, so that you can refer to it later
• The variable type which describes the type of data that the variable can hold.

The pattern for variable declaration is always

var name-of-variable type-of-variable

each part is separated by a space. The declaration must appear on a line on its own.

var is the keyword for a variable declaration. It must be in lower case and must be the first part of the variable declaration.

type-of-variable is the type to be used for the variable. At the moment this can only be a number type, int, or a string type, string.

name-of-variable is the name to be used for the variable. The variable name that is used must be a legal one according to the rules for variable names.

The programmer can choose the name of the variable, and the variable’s type. The variable name can be anything, provided the variable name follows the rules. The programmer chooses between int for a number type and string for a string type.

var distance_to_London int
var capitalOfScotland string

The Rules for Variable Names

When we say that a variable name is legal we mean that it must follow these rules. These rules are part of Go’s syntax rules.

Remember, the rules for variable names are

• You cannot use a keyword as a variable name.
• You cannot use spaces in your variables names, or any other symbols like ().
• You cannot use a package name for a variable name.
• You cannot start a variable name with a number.
• You cannot use the same name as another variable. Each variable name has to be unique.
• You can only use the letters a to z or A to Z or the numbers 0 to 9 or the underscore character _.

If a variable name does not follow these rules it is illegal and Go will not let you use it.

Assigning a New Value To a Variable

To assign or set, or change the value of a variable you need to use an equals = sign like this

age = 8

Which sets the value of age to 8. age must have been declared as

var age int

before the assignment can happen.

There is a pattern you can use to remember how to set the value of a variable. The pattern is

name-of-variable = new-value

First you use the name of the variable that you want to set, then an equals, = sign and then the new value for the variable.

You can only set a variable to a value that makes sense according to the type of the variable. If you tried to set the variable age to the string "eight" like this

age = "eight"

it will not work.

If a variable was declared as an int type then you can only store numbers in it. If the variable was declared as a string type you can only store strings in it.

The badvariables Program

Look at the badvariables program

 1package main
 2
 3import "fmt"
 4
 5func main() {
 6	var short_side int
 7	var long side int
 8	perimeter int
 9	var area string
10
11	short_side = 3
12	long_side % 8
13
14	fmt.Println("What shape am I?")
15	fmt.Print("Two of my sides are ")
16	fmt.Print(shortside)
17	fmt.Println( meters long.")
18	fmt.Print("Two of my sides are )
19	fmt.Print(long_side)
20	fmt.Println(" meters long.")
21	perimeter = 2*short_side + 2*long_side
22	fmt.Print("My area perimeter is ")
23	fmt.Print(perimeter)
24	fmt.Println(" meters.")
25	area = short_side * long_side
26	fmt.Print("My area is ")
27	fmt.Print(area)
28	fmt.Println(" meters square.")
29}

The badvariables program has lots of mistakes in it, so many it won’t run.

The corrected program is

 1package main
 2
 3import "fmt"
 4
 5func main() {
 6	var short_side int
 7	var long_side int
 8	var perimeter int
 9	var area int
10
11	short_side = 3
12	long_side = 8
13
14	fmt.Println("What shape am I?")
15	fmt.Print("Two of my sides are ")
16	fmt.Print(short_side)
17	fmt.Println( meters long.")
18	fmt.Print("Two of my sides are "")
19	fmt.Print("long_side)
20	fmt.Println(" meters long.")
21	perimeter = 2*short_side + 2*long_side
22	fmt.Print("My area perimeter is ")
23	fmt.Print(perimeter)
24	fmt.Println(" meters.")
25	area = short_side * long_side
26	fmt.Print("My area is ")
27	fmt.Print(area)
28	fmt.Println(" meters square.")
29}

The hellome Program

This is the hellobob program from the last lesson

 1package main
 2
 3import (
 4	"fmt"
 5)
 6
 7func main() {
 8	var name string
 9	var age int
10
11	name = "Bob"
12	age = 8
13
14	fmt.Println("The hellobob program shows you how to use variables.")
15	fmt.Println("")
16
17	fmt.Print("Hello, my name is ")
18	fmt.Print(name)
19	fmt.Println(".")
20	fmt.Print("I am ")
21	fmt.Print(age)
22	fmt.Println(" years old.")
23}

You are going to change it to create two new programs.

The hellome Program

The hellofriend Program

The hellofriend program prints my name and age
and my friend's name and age.

Hello, my name is Bob.
I am 8 years old.
My friend's name is Paul
Paul is 9 years old.