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JavaScript Notes: Comments, Operators, and Conditional Statements

1. Comments in JavaScript

  • Single-line Comment:
    Use // to comment out a single line of code. 
    // This is a single-line comment
let x = 10;  // This is also a comment
  • Multi-line Comment:
    Use /* ... */ to comment out multiple lines of code. 
    /*
 This is a 
 multi-line comment
*/
let y = 20;

2. Operators in JavaScript

Operators are symbols that perform operations on variables and values.

Types of Operators:

  1. Arithmetic Operators:

    • Used for mathematical calculations.
    • Examples: 
      let a = 10;
let b = 5;

console.log(a + b); // Addition: 15
console.log(a - b); // Subtraction: 5
console.log(a * b); // Multiplication: 50
console.log(a / b); // Division: 2
console.log(a % b); // Modulus: 0 (remainder)

  2. Assignment Operators:

    • Used to assign values to variables.
    • Examples: 
      let x = 10;  // Assign 10 to x
x += 5;      // x = x + 5 (x becomes 15)
x -= 2;      // x = x - 2 (x becomes 13)

  3. Comparison Operators:

    • Used to compare two values.
    • Examples: 
      let a = 10;
let b = 20;

console.log(a == b);  // Equal to: false
console.log(a != b);  // Not equal to: true
console.log(a > b);   // Greater than: false
console.log(a < b);   // Less than: true

  4. Logical Operators:

    • Used to combine two or more conditions.
    • Examples: 
      let a = 10;
let b = 20;

console.log(a > 5 && b > 15);  // Logical AND: true
console.log(a > 15 || b > 15); // Logical OR: true
console.log(!(a > 15));        // Logical NOT: true

  5. Increment/Decrement Operators:

    • Used to increase or decrease the value of a variable by 1.
    • Examples: 
      let count = 5;
count++;  // Increment: count becomes 6
count--;  // Decrement: count becomes 5

  6. Ternary Operator:

    • A shorthand for if-else statements.
    • Example: 
      let age = 18;
let result = (age >= 18) ? "Adult" : "Minor";
console.log(result); // Output: "Adult"

3. Conditional Statements in JavaScript

Conditional statements are used to perform different actions based on different conditions.

  1. if Statement:

    • Executes a block of code if the specified condition is true.
    • Example: 
      let age = 18;
if (age >= 18) {
    console.log("You are eligible to vote.");
}

  2. if-else Statement:

    • Executes one block of code if the condition is true, and another if it is false.
    • Example: 
      let age = 16;
if (age >= 18) {
    console.log("You are eligible to vote.");
} else {
    console.log("You are not eligible to vote.");
}

  3. if-else if-else Statement:

    • Executes multiple blocks of code depending on different conditions.
    • Example: 
      let marks = 85;

if (marks >= 90) {
    console.log("Grade A");
} else if (marks >= 75) {
    console.log("Grade B");
} else if (marks >= 50) {
    console.log("Grade C");
} else {
    console.log("Fail");
}