GR-CITRUS Special Project: Start Programming with Ruby

Hardware

You will need a GR-CITRUS board and a USB cable (Micro B type).

Software

We will be using Rubic for this project, so please familiarize yourself with the tool by referencing the Starting out with Rubic (Ruby Version) project page.

print

The serial class print is used to send a message to the connected PC when confirming the status of the program flow. Note that puts and p(“object”), both used frequently in Ruby, will generate syntax errors. Also, new generates a serial class instance, and argument 0 indicates use of USB.

    
    usb = Serial.new(0)
    usb.print("Hello")
    

(Result)

Hello

printIn

To insert a line feed, use printIn.

    
    usb = Serial.new(0)
    usb.println("Hello")
    usb.print("Hello")
    

(Result)

Hello

Hello

How to Handle Numerical Values

Declarations like those used in the C language are not necessary. However, when displaying the variable with print, because the argument is a character string, you will need to convert the string from numerical values using the to_s method.

    
    usb = Serial.new(0)
    a=7
    usb.println(a.to_s) # integer to string
    a+=1
    usb.println(a.to_s)
    

(Result)

7

8

How to Handle Character Strings

To put a character string in a variable, simply enclose the string in double quotation marks.

    
    usb = Serial.new(0)
    a="123"
    usb.println(a)
    a+="abc"
    usb.println(a)
    

(Result)

123

123abc

To include double quotations, enclose the entire string in single quotation marks.

    
    usb = Serial.new(0)
    a = '"a"'
    usb.println(a.to_s)
    

(Result)

"a"

Converting a Character String to a Numerical Value

To convert a character string to a numerical value, use the to_i method for integers and to_f method for floating points.

    
    usb = Serial.new(0)
    a ="123.001"
    usb.println(a)
    b = a.to_i + 456.12
    usb.println(b.to_s)
    b = a.to_f + 456.12
    usb.println(b.to_s)
    

(Result)

123.001

579.12

579.121

String Manipulation

Ruby string manipulation is really powerful. Here is part of a sample to give you an idea.

    
    usb = Serial.new(0)
    a ="aabbccddeeaabbccddee"
    usb.println(a)
    usb.println(a.length.to_s) #length
    usb.println(a.include?("ee").to_s) #include
    usb.println(a.upcase) #upcase
    usb.println(a.downcase) #downcase
    usb.println(a.gsub("a","A")) #gsub (replace)
    

(Result)

aabbccddeeaabbccddee

20

true

AABBCCDDEEAABBCCDDEE

aabbccddeeaabbccddee

AAbbccddeeAAbbccddee

How to Create an Array

Arrays are created without declarations. The index starts from 0, the same as with the C language.

    
    usb = Serial.new(0)
    a = [1,2,3,4]
    usb.println(a[2].to_s)
    

(Result)

3

Elements

Both numerical values and character strings can be elements, as well as a mix of both.

    
    usb = Serial.new(0)
    a = [1, "def", 3.14]
    usb.println(a[1].to_s)
    

(Result)

def

Adding or Joining Elements

Manipulating arrays in Ruby is really easy. This example shows how to add and join using unshift, push and concat.

    
    usb = Serial.new(0)
    a = ["pen"]
    a.unshift("apple")
    a.each do |n| 
        usb.print(n)
        usb.print(" ")
    end
    usb.println()
    b = ["pen"]
    b.push("pineapple")
    b.each do |n| 
        usb.print(n)
        usb.print(" ")
    end
    usb.println()
    b.concat(a)
    b.each do |n| 
        usb.print(n)
        usb.print(" ")
    end
    

(Result)

apple pen

pen pineapple

pen pineapple apple pen

each

The each method retrieves the array in the specified order.

    
    usb = Serial.new(0)
    a = [1, 2.3, "abc", [1,2]]
    a.each do |n|
        usb.println(n.to_s)
    end
    

(Result)

1

2.3

abc

[1,2]

while

This is an example of the well-used while. It is repeated if the conditional statement is true.

    
    usb = Serial.new(0)
    a = 5
    while a > 0 do
        usb.println(a.to_s)
        a = a - 1
    end
    

(Result)

5

4

3

2

1

times

This runs the operation for the specified number of times. If you don’t want to use variable a, you can eliminate |a|.

    
    usb = Serial.new(0)
    5.times do |a|
        usb.println(a.to_s)
    end
    

(Result)

0

1

2

3

4

for

This runs part of the range object (from 1…3). More specifically, it runs the partial operation the number of times described in the each method (described later) to retrieve the array.

    
    usb = Serial.new(0)
    for a in 1..3 do
      usb.println(a.to_s)
    end
    

(Result)

0

1

2

3