Add Conditions

Learning Objectives

• Understand conditional logic
• Master if, else if, and else statements
• Learn the ternary operator
• Use switch statements
• Apply conditions to real-world problems

Section 4.1: What's a Condition?

Conditional Logic

A condition is a statement that is either true or false. We use conditions to make decisions in our code.

let age = 18;

if (age >= 18) {
    console.log("You are an adult");
}

If Statement

The if statement executes code only if a condition is true:

if (condition) {
    // Code executes if condition is true
}

Example: Checking Age

let age = 20;

if (age >= 18) {
    console.log("You can vote");
}

If-Else Statement

Either execute one block OR another:

if (condition) {
    // Execute if true
} else {
    // Execute if false
}

Example: Even or Odd

let number = 7;

if (number % 2 === 0) {
    console.log("Even number");
} else {
    console.log("Odd number");
}

Section 4.2: Alternative Conditions

Comparison Operators

let x = 10, y = 5;

console.log(x > y);   // true (greater than)
console.log(x < y);   // false (less than)
console.log(x >= y);  // true (greater or equal)
console.log(x <= y);  // false (less or equal)
console.log(x === y); // false (equal value and type)
console.log(x !== y); // true (not equal)

Strict vs Loose Equality

console.log(5 == "5");   // true (loose equality)
console.log(5 === "5");  // false (strict equality)

// Always use === in JavaScript

Logical Operators

Both conditions must be true:

let age = 25;
let hasLicense = true;

if (age >= 18 && hasLicense) {
    console.log("You can drive");
}

At least one condition must be true:

let isWeekend = true;
let isHoliday = false;

if (isWeekend || isHoliday) {
    console.log("No work today!");
}

Reverses the condition:

let isRaining = true;

if (!isRaining) {
    console.log("Go outside");
} else {
    console.log("Stay inside");
}

Section 4.3: Add Additional Logic

If-Else If-Else Chain

Handle multiple conditions:

let score = 75;
let grade;

if (score >= 90) {
    grade = "A";
} else if (score >= 80) {
    grade = "B";
} else if (score >= 70) {
    grade = "C";
} else if (score >= 60) {
    grade = "D";
} else {
    grade = "F";
}

console.log("Grade: " + grade);

Nested Conditions

Conditions inside conditions:

let age = 25;
let hasLicense = true;

if (age >= 18) {
    if (hasLicense) {
        console.log("You can drive");
    } else {
        console.log("You need a license");
    }
} else {
    console.log("You must be 18 to drive");
}

Ternary Operator (Conditional Expression)

Shorthand for simple if-else:

// Standard if-else
let status;
if (age >= 18) {
    status = "adult";
} else {
    status = "minor";
}

// Using ternary operator
let status = age >= 18 ? "adult" : "minor";

Syntax: condition ? valueIfTrue : valueIfFalse

let message = score >= 50 ? "Passed" : "Failed";
let access = isAdmin ? "Full access" : "Limited access";
let discount = quantity > 10 ? "20%" : "10%";

Section 4.4: Multiple Choices

Switch Statement

Use switch when you have many specific options:

let day = 3;
let dayName;

switch (day) {
    case 1:
        dayName = "Monday";
        break;
    case 2:
        dayName = "Tuesday";
        break;
    case 3:
        dayName = "Wednesday";
        break;
    case 4:
        dayName = "Thursday";
        break;
    case 5:
        dayName = "Friday";
        break;
    default:
        dayName = "Weekend";
}

console.log(dayName);  // Wednesday

Switch with Multiple Cases

let grade = "B";

switch (grade) {
    case "A":
    case "B":
        console.log("Excellent work!");
        break;
    case "C":
        console.log("Good work!");
        break;
    case "D":
    case "F":
        console.log("Need improvement");
        break;
    default:
        console.log("Invalid grade");
}

If vs Switch

Use if-else for:

• Complex conditions
• Range comparisons (>, <, >=, <=)
• Boolean logic (&&, ||)

Use switch for:

• Exact matches
• Many specific values
• Cleaner code with multiple cases

Coding Challenges

Challenge 4.1: Following Day

Task: Write a program that:

• Asks for a day number (1-7)
• Displays the day name and the next day

Example Output:

Enter day (1-7): 3
Today: Wednesday
Tomorrow: Thursday

Challenge 4.2: Number Comparison

Task: Compare two numbers and display:

• Which is larger
• Which is smaller
• If they're equal

Example Output:

Enter first number: 10
Enter second number: 25
25 is larger
10 is smaller

Challenge 4.3: Number of Days in a Month

Task: Ask for a month number and display how many days it has

• Months with 31 days: 1, 3, 5, 7, 8, 10, 12
• Months with 30 days: 4, 6, 9, 11
• February: 28 days (29 in leap years)

Challenge 4.4: Adding Seconds to Time

Task: Convert seconds into hours, minutes, and seconds

Example:

Input: 3661 seconds
Output: 1 hour, 1 minute, 1 second

Key Takeaways

✅ Conditions control program flow
✅ Use === for strict equality comparisons
✅ Combine conditions with logical operators (&&, ||, !)
✅ Chain conditions with else if
✅ Use ternary operator for simple decisions
✅ Use switch for multiple specific values

Quiz Questions

• What does === do differently from ==?
• Explain the AND (&&) operator with an example
• When would you use a switch instead of if-else?
• What does the ternary operator do?
• How do you check if a number is between 10 and 20?

Next Module: Module 5 - Repeat Statements