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# Computer Science Cheatsheet

## Programming Concepts

### Variables and Data Types

Variables hold data and data types define the kind of data a variable can hold.

variable declaration

x = 10

data types

string = "hello"

integer = 42

float = 3.14

boolean = true

array = [1, 2, 3]

hash = { name: "John", age: 25 }


# Functions

Functions are reusable code blocks that take input parameters and perform a set of instructions.

function declaration

def greet(name)

puts "Hello, #{name}!"

end

function call

greet("John")


# Loops

Loops allow you to repeatedly execute code.

while loop

i = 0

while i < 5 do

puts i

i += 1

end

for loop

for i in 0..4

puts i

end

each loop

[1, 2, 3].each do |i|

puts i

end


# Conditionals

Conditionals execute code based on whether a condition is true or false.

if statement

x = 10

if x > 5

puts "x is greater than 5"

end

else statement

if x < 5

puts "x is less than 5"

else

puts "x is greater than or equal to 5"

end

case statement

grade = "A"

case grade

when "A"

puts "Great job!"

when "B"

puts "Good job!"

else

puts "Try harder next time!"

end


# File Manipulation

Reading and writing files is a common task in programming.

writing to a file

File.open("file.txt", "w") do |file|

file.write("Hello, world!")

end

reading from a file

File.open("file.txt", "r") do |file|

puts file.read

end


Resources

- [Ruby Documentation](https://www.ruby-lang.org/en/documentation/)
- [Ruby on Rails](https://rubyonrails.org/)
- [Learn Ruby the Hard Way](https://learnrubythehardway.org/)
- [Ruby Monk](https://rubymonk.com/)