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Ruby

https://ruby-doc.org/ ri # documentation from the command line

  • An object-oriented programming language.
  • No "primitives".

print vs puts

  • first introduced: puts and print;
  • puts 后会空一行，print 是 inline.
  • 有点像 Java 的 print 和 println;

variables

  • when creating a variable in ruby, we ...

    • give the name of the variable,
    • multiple words separated by underscore _, (aka snake_case)
    • what to store inside the variable.

  • if we are using text + variable to display information, we need to wrap the whole statement with parantheses.

  • 可以随时 update variable, just set the variable to the new value.

Data Types

  • string: plain text
  • numbers: including integers, floating point numbers (decimals)
  • boolean: true or false
  • nil: has no value

Strings

  • to type out quotation mark, can use a backslash \.

  • \n will print a new line.

  • string methods (aka string functions) are methods we can call on strings to modify or give information about the string.

  • some methods include ...

    • .upcase(): converts all characters to uppercase

    • .downcase(): converts all chracters to lowercase

    • .strip(): removes white spaces

    • .length(): returns the length of the string

    • .include? "": returns true or false

    • .index(): returns the index of the character(s)

Math & Numbers

  • arithmetics on numbers ...

    • addition, subtraction, multiplication, division
    • n**m: exponents
    • %: 老朋友了。

  • in ruby, to print a number with string (two different data types in general) will need to convert the number to a string by using .to_s.

  • and to convert to integer (say getting a user input of number), can be done by using .to_i, and .to_f for float.

  • numbers methods ...

    • .abs(): returns absolute val
    • .round(): rounds the number
    • .ceil() / .floor(): returns rounding of the higher / lower number

  • can use functions from the Math class ...

    • Math.sqrt(n): returns the square root of the number n

  • operation performed between integer and integer will return integer, between integer and float will return a float.

User Input

  • gets: takes an user input (can be stored in a variable for later use)
  • whenever the user press "enter" after gets, ruby will take it as a new line.
  • .chomp() can be used to get rid of this behavior.
  • ruby automatically converts whatever the user entered into a string.

Arrays

  • can store different data types inside the array.
array_name = Array[element1, element2, element3 ...]
  • can access backwards by using negative values (这点和 python 一样).
  • can also decalre an array without initializing.
array_name = Array.new
  • array methods 大致和 string methods 一样。
  • can use .sort() as well.
  • cannot use sort on an array that contains different data types though because ruby won't know how to compare them.

Hashes

  • Object -- key value pairs.
  • aka dictionaries (和 python 一样).
  • keys need to be unique.
hash_name = {
  key1 => value1,
  key2 => value2,
  :key3 => value3
}

hash_name[:key3] # works
hash_name[key1] # works

Methods

def method_name

end

# with param & default param
def method_name(param1="default", param2 ...)

end

Return

  • like other programming languages, code after return statement won't get executed.
  • can return multiple values (essentially like returning an array).

if statements

  • keywords: if, else, and, or, elsif
  • elsif: else if
  • comparison: >=, >,<=, <, ==, !=

Case Expressions (Skipped)

While Loops

  • loop through the code as long as the condition remains true.
while condition
  # code
end

For Loops

  • allows us to loop through a collection.
for element in array
  # code
end
  • can also use each.
array.each do |element|
  # code
end

Reading Files

File.open(name_of_file, mode) do |variable_name|

# mode: read -> r,