🔁 Control Flow in JavaScript: If, Else, and Switch Explained

Introduction: What Is Control Flow?

In real life, we make decisions all the time:

• If it’s raining, take an umbrella

• Else, go outside freely

• If today is Sunday, relax

• Else, go to work

Programming works the same way.

👉 Control flow means deciding which code should run and which should not, based on conditions.

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Why Control Flow Is Important

Without control flow:

• Every line of code would run

• Programs couldn’t make decisions

• Apps wouldn’t react to user input

Control flow allows JavaScript to think logically.

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The if Statement

The if statement runs code only when a condition is true.

Example: Checking Age

let age = 20;

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

✔️ Condition is checked

✔️ If true → code runs

✔️ If false → code is skipped

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The if-else Statement

Use if-else when there are two possible outcomes.

Example: Pass or Fail

let marks = 35;

if (marks >= 40) {
  console.log("You passed");
} else {
  console.log("You failed");
}

👉 Only one block will run.

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The else if Ladder

Use else if when there are multiple conditions.

Example: Positive, Negative, or Zero

let number = -5;

if (number > 0) {
  console.log("Positive number");
} else if (number < 0) {
  console.log("Negative number");
} else {
  console.log("Zero");
}

How this runs:

1. Check first condition

2. If false → move to next

3. Stops as soon as one condition is true

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The switch Statement

switch is used when:

• You compare one value

• Against many fixed options

Example: Day of the Week

let day = 3;

switch (day) {
  case 1:
    console.log("Monday");
    break;
  case 2:
    console.log("Tuesday");
    break;
  case 3:
    console.log("Wednesday");
    break;
  default:
    console.log("Invalid day");
}

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Why break Is Important in Switch

Without break, JavaScript will:

• Continue executing the next cases

• Even if the correct case is found

case 3:
  console.log("Wednesday");
  break;

👉 break stops execution once a match is found.

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When to Use if-else vs switch

Use if-else when:

• Conditions involve ranges (>, <, >=)

• Logic is more flexible

Example:

if (marks > 90) { }

Use switch when:

• Comparing exact values

• Code becomes cleaner

Example:

switch(day) { }

✔️ Readability matters more than rules.

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🧪 Practice Assignment

1️⃣ Positive, Negative, or Zero

let num = 0;

if (num > 0) {
  console.log("Positive");
} else if (num < 0) {
  console.log("Negative");
} else {
  console.log("Zero");
}

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2️⃣ Day of the Week Using Switch

let day = 5;

switch (day) {
  case 1:
    console.log("Monday");
    break;
  case 2:
    console.log("Tuesday");
    break;
  case 3:
    console.log("Wednesday");
    break;
  case 4:
    console.log("Thursday");
    break;
  case 5:
    console.log("Friday");
    break;
  default:
    console.log("Invalid day");
}

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Final Thoughts

Control flow is the brain of your program.

Once you understand:

• if

• else

• switch

You can:

• Build real logic

• Handle user decisions

• Write meaningful programs