Understanding Arrays & Syntax

Arrays

• Arrays store multiple values in a single variable
• [] should always be included in array declarations
• Elements are contained in [elements]
• [elements] = {index} indicates the index of the elements
• Arrays are collections of elements that must be all of the same data type
• Arrays store multiple values of the same type in a contiguous memory block
• Array indexing starts at 0

Syntax

• [10] declares an integer with 10 elements
• Data type variable [3] = {“1”, “2”, “3” }; declares an integer with an index/value
• If counting the index value, the elements should be the same number
• Data type variables [] = new data type [element value] declares an integer without a value
• INDEX represents the position of the value
• Zero-Based Indexing means the first element is at index 0, the second at index 1, and so on

Identifying/Reading Array Elements

• Identify [index] is how array elements are read

Declaration Without Initialization

• int[] numbers; is an example of declaring an array without initializing it

Declaration With Initialization

• int[] numbers = new int[5]; declares and initializes an array

Declaration and Initialization with Specific Values

• int[] numbers = {10, 20, 30, 40, 50}; declares and initializes an array with specific values
• int firstNumber = numbers[0]; gets the first element (10)
• numbers[1] = 25; sets the second element to 25 by reassigning the variable

Arithmetic Operators

• Arithmetic operators are symbols that perform basic mathematical operations like addition, subtraction, multiplication, and so on

Relational Operators

• Relational operators check the relation between two operands
• These operators are also known as "Comparison Operators"
• Comparison Operators makes a comparison between two operands
• The result of relational operators is always a Boolean value
• A value involved in an operation is called an OPERAND
• == is equal to, and checks whether two given operands are equal or not
• If the left-hand operand equals the right-hand operand, the operators return true; otherwise, results are false
• != is not equal to, and checks whether the two given operands are not equal
• This function is the opposite of the == function
• The operator returns true if the left-hand operand is not equal to the right-hand operand, and returns false otherwise
• => is equal to or greater than, and checks whether the left-hand side is equal to or greater than the right-hand side
• The operators return true if the left side is equal to or greater than the right side and returns false otherwise
• =< is equal to or less than, and checks whether the left-hand side is equal to or less than the right-hand side
• This is the opposite of =>
• The function returns true if the left-hand side is greater than or equal to the right-hand side, and returns false otherwise
• > is greater than, and checks whether the left-hand side is greater than the right-hand side
• The function returns true if the left-hand side is greater than the right-hand side, and returns false otherwise
• < is less than, and checks whether the left-hand side is less than the right-hand side
• This is the opposite of >
• The function returns true if the left-hand side is less than the right-hand side, and returns false otherwise

Expressions and Operands

• Expression: Operation & Operands
• Operands: Value, Variables & Quantity
• Operators include +, -, ++, --, %, /, *, ==, !=, >, <, =>, =<

Logical Operators

• Logical operators are used in programming to evaluate conditions and check if certain conditions are true or false, and give results based on that
• The result is always Boolean
• true if the condition is met, or
• false if the condition is not met

Types of Logical Operators

• Logical AND (&&) checks if both conditions are true
• If both are true, the result is true; otherwise, it is false
• Logical OR (||) checks if at least one of the conditions is true
• If at least one is true, the result is true; if both are false, the result is false
• Logical NOT (!) reverses the boolean value of a condition
• If a condition is true, applying ! makes it false, and vice versa

String Methods

• String is a reference data type
• This means it is not a simple data type (like numbers or characters)
• Strings store one or more characters (e.g., words, sentences)

Common String Methods

• .equals("") compares two strings and checks if they are exactly the same (case-sensitive)
• .equalsIgnoreCase("") compares two strings but ignores whether the letters are uppercase or lowercase
• .length() returns the number of characters in a string
• .charAt(index) returns the character at a specific position (index) in the string
• Indexes start at 0
• .indexOf("") finds the position (index) of the first occurrence of a specific character or substring
• .isEmpty() checks if a string is empty (has no characters)
• .toUpperCase() converts all characters in a string to uppercase
• .toLowerCase() converts all characters in a string to lowercase
• .replace(oldChar, newChar) replaces all occurrences of a specific character or substring with another character or substring
• .toString() converts other objects or arrays into a string format

If Statements

• An if statement checks a condition (like a question: “Is this true or false?”)
• If the condition is true, a block of code will run; if it's false, the code does nothing
• Condition: A statement that can be true or false (e.g., x > 5 or age == 18)
• Code block: The code inside {} will only run if the condition is true
• One block of code will run if the condition is true
• A different block of code will run if the condition is false
• A nested if statement means putting one if statement inside another, which is useful for checking multiple conditions
• An else-if statement lets you check multiple conditions
• If the first condition is false, it checks another condition
• An if-else statement gives you two options

Logical Flow

• if statements handle one condition
• if-else handles two possibilities (true or false)
• nested if allows checking conditions within conditions
• else-if handles multiple possibilities

Boolean Expressions

• The conditions inside if statements are boolean expressions
• Boolean expressions meaning they evaluate to either true or false

Logical Operators

• Multiple conditions can be combined using logical operators
• && (AND): Both conditions must be true
• || (OR): At least one condition must be true
• ! (NOT): Reverses the boolean value of the condition