Control Flow in Programming (JavaScript)

1. Introduction: What is Control Flow in Programming?

Imagine a normal day in your life.

You wake up and think:

• If it is morning, I will brush my teeth

• If it is Sunday, I will rest

• If it is Monday, I will go to work

Your brain is constantly making decisions.

Programming works the same way.

A computer program also needs to decide:

• Should this code run?

• Or should another code run?

• Or should it skip something?

This process is called Control Flow.

Definition

Control Flow determines the order in which instructions are executed in a program.

Without control flow, a program would execute every line from top to bottom with no decision-making.

❊Example Without Control Flow

console.log("Wake up");
console.log("Go to gym");
console.log("Go to office");
console.log("Sleep");

The program will run every line.

But what if today is Sunday?

You might not want to go to the office.

This is where control flow statements come into play.

❊ Types of Control Flow Statements

The most common ones are:

1. if statement

2. if-else statement

3. else-if ladder

4. switch statement

These help programs make decisions.

2. The if Statement

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

Syntax

if (condition) {
    // code runs if condition is true
}

❊ Real Life Example

Imagine a school rule:

If a student’s marks are greater than 40, they pass.

let marks = 50;

if (marks > 40) {
  console.log("You passed the exam");
}

Step-by-Step Execution

1. Program reads the value of marks

2. It checks the condition marks > 40

3. If the condition is true, the code inside {} runs

4. If the condition is false, the program skips it

Example Output

You passed the exam

When the condition is false

let marks = 30;

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

Output:

(no output)

Because the condition is false.

3. The if-else Statement

Sometimes we want the program to do something else if the condition is false.

That is where if-else is used.

Syntax

if (condition) {
   // runs if condition is true
} else {
   // runs if condition is false
}

❊ Real Life Example

At a movie theatre:

• If age ≥ 18 → Allowed

• Else → Not allowed

Example

let age = 16;

if (age >= 18) {
  console.log("You can watch the movie");
} else {
  console.log("You are not allowed");
}

❊ Step-by-Step Execution

1. Program checks age >= 18

2. If true → first block runs

3. If false → else block runs

Output

You are not allowed

4. The Else If Ladder

Sometimes there are multiple conditions.

Example: grading system

Marks	Grade
90+	A
75+	B
50+	C
<50	Fail

This is where else-if ladder is useful.

Syntax

if (condition1) {

} else if (condition2) {

} else if (condition3) {

} else {

}

Example

let marks = 82;

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");
}

⤑ Step-by-Step Execution

Marks = 82

1. Check marks >= 90 → false

2. Check marks >= 75 → true

3. Program prints Grade B

4. Remaining conditions are skipped

Output

Grade B

5. The Switch Statement

The switch statement is used when there are many possible fixed values.

It is commonly used for:

• menus

• days of week

• months

• options

⤑ Syntax

switch(expression) {

  case value1:
    code
    break;

  case value2:
    code
    break;

  default:
    code
}

⤑ Example: Day of 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");
}

⤑ Step-by-Step Execution

1. day = 3

2. Switch checks cases

3. case 3 matches

4. Prints Wednesday

❊ Understanding break in Switch

break stops execution.

Without break, the program continues executing the next cases.

⤑ Example Without break

let day = 2;

switch(day) {

  case 1:
    console.log("Monday");

  case 2:
    console.log("Tuesday");

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

Output

Tuesday
Wednesday

This happens because there is no break.

6. When to Use Switch vs If-Else

⤑ Use if-else when:

• conditions are ranges

Example:

marks > 90
age >= 18
temperature > 30

⤑ Use switch when:

• checking specific values

Example:

day = Monday
role = admin
menu option = 1

⤑ Example

Good for if-else

if (marks > 90)

Good for switch

switch(day)

❊ Comparison Table

Feature	if-else	switch
Range conditions	Yes	No
Exact values	Yes	Yes
Readability with many cases	Hard	Easier
Common use	logic	menus/options

❊ Conclusion

Control flow is one of the most fundamental concepts in programming.

It allows programs to:

• make decisions

• run different code paths

• handle real-world logic

The most important control flow statements are:

• if

• if-else

• else-if ladder

• switch

Understanding when to use each of them will make your programs cleaner and easier to understand.

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