Variables and Data Types • Variables are named containers for storing data values like numbers or text. • They let you store and reuse information, making your code dynamic and flexible. • Use let or const to declare a variable and assign it a value. • Use them to hold user input, calculations, or any information your program needs.

Key points: - Variables hold data. - Use let for changing values. - Use const for fixed values. - Data has types: strings, numbers, booleans, etc. - Choose descriptive variable names.

Example: javascript let userName = "Alice"; const age = 30; console.log(userName + " is " + age + " years old.");

Operators and Expressions • Operators perform operations on values, while expressions combine values and operators. • They allow you to manipulate data, perform calculations, and make comparisons. • Arithmetic operators (+, -, *, /) and comparison operators (>, <, ==) are common. • Use them for calculations, logical decisions, and combining pieces of data.

Key points: - Operators perform actions on data. - Expressions are combinations of values and operators. - Arithmetic operators: +, -, *, /. - Comparison operators: ==, !=, >, <, >=, <=. - Logical operators: &&, ||, !.

Example: javascript let price = 10; let quantity = 5; let totalCost = price * quantity; console.log("The total cost is: " + totalCost);

Control Flow: Conditional Statements • Conditional statements let your code make decisions based on specific conditions. • They ensure your program runs different code blocks depending on the situation. • Use if, else if, and else to check conditions and execute code blocks. • Use them to handle different user inputs, errors, or states within your application.

Key points: - Control flow guides execution path. - if executes code if condition is true. - else if checks another condition. - else executes if all preceding conditions are false. - Conditions typically use comparison operators.

Example: javascript let score = 75; if (score >= 90) { console.log("Excellent!"); } else if (score >= 70) { console.log("Good job!"); } else { console.log("Keep practicing."); }

Loops: Iterating Through Code • Loops allow you to repeat a block of code multiple times automatically. • They are essential for processing lists of data or performing repetitive tasks efficiently. • Use for or while loops to execute code as long as a condition remains true. • Use them to display items from an array, process data records, or repeat actions.

Key points: - Loops repeat code blocks. - for loop is good for known iterations. - while loop repeats as long as a condition is true. - Avoid infinite loops by ensuring conditions eventually become false. - Loops make repetitive tasks easy.

Example: javascript for (let i = 0; i < 5; i++) { console.log("Iteration number: " + (i + 1)); }

Quick quiz: 1. Which of the following declares a variable that can be reassigned its value later? 2. What will be the output of the following expression: 10 + '5' - 2? 3. Consider the following code snippet: javascript let x = 5; if (x > 10) { console.log('A'); } else if (x < 0) { console.log('B'); } else { console.log('C'); }

What will be logged to the console? 4. Which loop statement is best suited for iterating a specific number of times, where the number of iterations is known beforehand?