Nested Conditionals Lesson

What are Nested Conditionals?

Nested conditionals are conditionals within conditionals. They allow us to check multiple conditions in a hierarchical way, where the result of one condition determines which other conditions we check next.

Pseudocode Structure

Here’s the basic structure of nested conditionals:

if (condition) {
    if (condition) {
        // code
    } else {
        // code
    }
} else {
    if (condition) {
        // code
    } else {
        // code
    }
}

In this structure, we check an initial condition. Depending on whether it’s true or false, we move to one segment of code and check another conditional. Going down one path means you do not go down another.

Example 1: Game Level Completion

Let’s look at a real-world example. Imagine we’re playing a game that checks if we’ve completed a level by satisfying two requirements:

TIME is less than 3 seconds
SCORE is greater than 1000

If both conditions are met, we add 3 lives and increase the level.

// Initial game state
let score = 1200;
let time = 2.5;
let level = 2;
let lives = 3;

console.log(`Starting state: Score=${score}, Time=${time}, Level=${level}, Lives=${lives}`);

// Simple condition (not complete yet)
if (time < 3 && score > 1000) {
    lives = lives + 3;
    level = level + 1;
    console.log("Both conditions met! +3 lives, +1 level");
}

console.log(`Final state: Score=${score}, Time=${time}, Level=${level}, Lives=${lives}`);

Problem: What if the conditions aren’t met?

The above code doesn’t tell the game what to do if:

Only one condition is met
Neither condition is met

Let’s fix this with nested conditionals!

Complete Nested Conditional Example

// Initial game state
let score = 1200;
let time = 4.2;
let level = 2;
let lives = 3;

console.log(`Starting state: Score=${score}, Time=${time}, Level=${level}, Lives=${lives}`);

// Complete nested conditional
if (time < 3 && score > 1000) {
    // Both conditions met
    lives = lives + 3;
    level = level + 1;
    console.log("Both conditions met! +3 lives, +1 level");
} else {
    // At least one condition was NOT met
    if (time < 3 || score > 1000) {
        // At least one condition is met
        lives = lives + 1;
        console.log("One condition met! +1 life");
    } else {
        // Neither condition is met
        lives = lives - 1;
        console.log("No conditions met! -1 life");
    }
}

console.log(`Final state: Score=${score}, Time=${time}, Level=${level}, Lives=${lives}`);

🤔 Prediction Exercise

Before you ran the code above, what did you predict would happen?

Answer: Since time = 4.2 (NOT less than 3) and score = 1200 (IS greater than 1000), only ONE condition is met. So we take the else branch, then the inner if branch is true, giving us +1 life. The player ends with 4 lives and stays at level 2.

Example 2: Temperature and Weather Advisory System

Let’s look at another real-world application: a weather advisory system that gives recommendations based on temperature and whether it’s raining.

let temperature = 85;
let isRaining = false;

console.log(`Current conditions: ${temperature}°F, Raining: ${isRaining}`);
console.log("\nWeather Advisory:");

if (temperature > 80) {
    // It's hot
    if (isRaining) {
        console.log("It's hot and rainy - stay hydrated and bring an umbrella!");
    } else {
        console.log("It's hot and sunny - wear sunscreen and stay hydrated!");
    }
} else {
    // It's not hot
    if (isRaining) {
        console.log("It's cool and rainy - bring a jacket and umbrella!");
    } else {
        console.log("It's cool and clear - perfect weather for outdoor activities!");
    }
}

Try It Yourself!

Modify the temperature and isRaining values in the cell above and run it again to see different advisories.

Example 3: Student Grade Calculator

Here’s a more complex example that determines a student’s grade and eligibility for honors based on their test score and homework completion.

let testScore = 88;
let homeworkCompleted = 0.95;  // 95% of homework completed

console.log(`Test Score: ${testScore}`);
console.log(`Homework Completion: ${homeworkCompleted * 100}%`);
console.log("\nGrade Evaluation:");

if (testScore >= 90) {
    // A grade territory
    if (homeworkCompleted >= 0.9) {
        console.log("Grade: A");
        console.log("Status: Honors eligible! Excellent work!");
    } else {
        console.log("Grade: A");
        console.log("Status: Great test score, but complete more homework for honors.");
    }
} else {
    // Below A grade
    if (testScore >= 80) {
        // B grade territory
        if (homeworkCompleted >= 0.9) {
            console.log("Grade: B+");
            console.log("Status: Good work! A little more effort on tests for honors.");
        } else {
            console.log("Grade: B");
            console.log("Status: Solid performance. Focus on homework completion.");
        }
    } else {
        // Below B grade
        console.log("Grade: C or below");
        console.log("Status: Let's meet to discuss how to improve your grade.");
    }
}

🎯 Quick Check: Test Your Understanding

What would happen in the grade calculator if:

testScore = 92 and homeworkCompleted = 0.85?
testScore = 85 and homeworkCompleted = 0.95?
testScore = 75 and homeworkCompleted = 0.80?

Try changing the values above and running the code to check your predictions!

Real-World Applications

Nested conditionals are used everywhere in programming:

Video Games: Checking player state, inventory, and abilities
E-commerce: Determining shipping costs, discounts, and eligibility
Social Media: Filtering content based on user preferences and privacy settings
Banking Apps: Validating transactions based on balance, limits, and security checks
Fitness Apps: Providing workout recommendations based on fitness level and goals

The key is that nested conditionals let you make hierarchical decisions where one choice determines what other choices you need to make next.

Summary

Nested conditionals are conditionals inside other conditionals
They allow us to create complex decision-making logic
Each path through the nested structure is exclusive - you only go down one path
Use nested conditionals when the conditions you need to check depend on previous conditions
Remember to handle all possible cases (including edge cases!)