Glossary

Data Types

• Boolean - An object that represents a logical truth value: true and false.
• Data Type - A classification of an object that determines its possible values and methods.
• Floating Point Number - A number with a decimal point.
• Integer - A number without a decimal point.
• Method - A procedure associated with an object; methods are the "verbs" of the language.
• Nil - A one-of-a-kind object that represents a lack of data: nil.
• Object - Ruby's representation of data; objects are the "nouns" of the language.
• Programming Language - A formal computer language designed to communicate instructions to a machine.
• String - A sequence of characters enclosed in quotation marks; Ruby's representation of text.

Your First Program

• Error - A type of software bug the renders code incapable of execution; an error violates rules of the programming language.
• Ruby Interpreter - The program that parses and executes Ruby code.
• Software Bug - An error or flaw in a computer program that causes an incorrect or unintended result.
• Stack Trace - A list of code locations whence an error originates.

Variables

• Assignment Operator - An operator (=) used to assign variable names to values.
• Comment - An annotation ignored by the interpreter.
• Snake Case - The practice of writing compound words or phrases in lowercase and connected by underscores rather than spaces.
• Variable - A label that refers to a value stored in memory.
• Variable Assignment - The assignment of a variable name to a value.

Numbers

• Expression - A combination of objects, methods, variables, and/or operators that evaluates to another value; a self-contained chunk of valid code.
• Modulo Operator - An operator (%) that returns the remainder of division.
• Operator - A type of method that uses a special, more intuitive syntax.
• Operand - The quantities with which an operation is performed.

Numerical Methods

• ceil - Rounds a float up.
• even? - Returns a boolean indicating whether an integer is even.
• floor - Rounds a float down.
• gcd(arg) - Returns the greatest common divisor.
• lcm(arg) - Returns the least common multiple.
• odd? - Returns a boolean indicating whether an integer is odd.
• round - Rounds a float to the nearest integer.
• to_i - Rounds a float down and converts it to an integer.
• to_f - Converts an integer to a float.
• to_s - Converts any object to a string.

Methods

• Argument - The input of a method. An argument is passed to a method within parentheses. Commas separate multiple arguments.
• Helper Method - A method that helps another method perform its task by managing a subtask.
• Method - A group of expressions that returns a value; the "verbs" of Ruby.
• Method Body - The code between the def statement and end in a method definition; the subroutine that the method definition encapsulates.
• Method Definition - The assignment of a subroutine to a name that can be invoked.
• Method Invocation - A call to the Ruby interpreter to execute a method.
• Parameter - A variable declared upon method definition that represents an argument passed in to a method upon invocation.
• Receiver - The object upon which the method is called.
• Return Value - The output of a method; the value to which the method evaluates.
• Subroutine - A set of instructions that perform a specific operation.
• Separation of Concerns - The principle of separating a program into distinct sections that each address a specific concern.
• return - A Ruby keyword that immediately returns the value of the subsequent expression.
• Unreachable Code - Code that can never be executed.

Data Structures

• Array - An ordered, zero-indexed collection of objects.
• Data Structure - A format for organizing and storing data.
• Nested Array - An array that includes another array; synonymous with two-dimensional array.
• Two-Dimensional Array - An array that includes another array; synonymous with nested array.

Array-Exclusive Methods

• first - Returns the first element of the array.
• join(separator) - Combines every element of an array into a string and returns the result; splices the elements together with an optional argument (the separator); does not modify the original array.
• last - Returns the last element of the array.
• pop - Removes an element from the end of the array and returns the removed element; modifies the original array.
• push(arg) - Adds an element to the end of the array and returns the array; modifies the original array.
• shift - Removes an element from the front of the array and returns the removed element; modifies the original array.
• sort - Sorts the array alphabetically or numerically and returns the result; does not modify the original array.
• unshift(arg) - Adds an element to the front of the array and returns the array; modifies the original array.

String-Exclusive Methods

• downcase - Replaces all uppercase letters with their lowercase counterparts and returns the result; does not modify the original string.
• split(delimiter) - Divides a string into an array along the delimiter and returns the result; the default delimiter is ' '; does not modify the original string.
• upcase - Replaces all lowercase letters with their uppercase counterparts and returns the result; does not modify the original string.

Array and String Methods

• concat(arg) - Concatenates two arrays or two strings and returns the resulting concatenation; modifies the receiver.
• include?(arg) - Returns a boolean value indicating whether the argument is included in the array or string.
• length - Returns the length of an array or string.
• reverse - Reverses the order of the array or string and returns the result; does not modify its receiver.
• + - Concatenates two strings or two arrays and returns the resulting concatenation; does not modify the left argument.
• << - The shovel operator; equivalent to push for arrays, equivalent to concat for strings; modifies the receiver.
• [](arg) - Accesses and returns one or more elements in an array or string.

Control Flow

• Conditional Statement - A control structure that instructs the interpreter to execute different branches of code depending on whether a condition is true or false.
• Control Flow - The order in which instructions are executed within a program.
• Control Structure - A block of code that alters the control flow based on analysis of given parameters.
• Iteration - The act of repeating a procedure and each repetition itself.
• Loop - A control structure that instructs the Ruby interpreter to repeatedly execute a section of code while a condition holds.
• Short-Circuit Evaluation - When the second operand of a logical operator is evaluated only if the first operand does not suffice to determine the value of the expression.

Comparison Operators

• > - Greater than; returns a boolean.
• < - Less than; returns a boolean.
• >= - Greater than or equal to; returns a boolean.
• <= - Less than or equal to; returns a boolean.
• == - Equal to; returns a boolean.
• != - Not equal to; returns a boolean.
• <=> - The spaceship operator; returns -1 if less than, 0 if equal to, 1 if greater than.

Logical Operators

• && - The logical AND.
• || - The logical (inclusive) OR.
• ! - The logical NOT.