Control Flow

Control flow refers to the order in which statements are executed in a program. Programming languages provide various constructs to manage this order, allowing for conditional execution, repetition, and structured execution of code blocks.

Conditional Statements

Conditional statements allow you to execute different blocks of code based on whether a certain condition is true or false.

The if Statement

The if statement executes a block of code only if a specified condition is true.

if (temperature > 30) {
    console.log("It's a hot day!");
}
            

The if...else Statement

The if...else statement executes one block of code if the condition is true, and another block if the condition is false.

let score = 75;
if (score >= 60) {
    console.log("You passed!");
} else {
    console.log("You need to improve.");
}
            

The if...else if...else Statement

This structure allows for multiple conditions to be checked in sequence.

let grade = 85;
if (grade >= 90) {
    console.log("Grade: A");
} else if (grade >= 80) {
    console.log("Grade: B");
} else if (grade >= 70) {
    console.log("Grade: C");
} else {
    console.log("Grade: D or lower");
}
            

The switch Statement

The switch statement is a multi-way branching statement that compares a variable to a list of values and executes code based on the first match.

let day = "Monday";
switch (day) {
    case "Monday":
        console.log("Start of the week.");
        break;
    case "Friday":
        console.log("End of the week!");
        break;
    default:
        console.log("Just another day.");
}
            

The break keyword is crucial within a switch statement to prevent "fall-through" to the next case.

Logical Operators

Logical operators are used to combine or modify conditions within control flow statements.

• && (Logical AND): True if both conditions are true.
• || (Logical OR): True if at least one condition is true.
• ! (Logical NOT): Reverses the boolean value of a condition.

let isLoggedIn = true;
let isAdmin = false;

if (isLoggedIn && isAdmin) {
    console.log("Welcome, Admin!");
} else if (isLoggedIn) {
    console.log("Welcome, User!");
} else {
    console.log("Please log in.");
}
            

Branching within Loops

Control flow statements also play a vital role in controlling loops.

• break: Exits the current loop entirely.
• continue: Skips the rest of the current iteration and proceeds to the next.

for (let i = 0; i < 10; i++) {
    if (i === 3) {
        continue; // Skips printing 3
    }
    if (i === 7) {
        break; // Exits the loop when i reaches 7
    }
    console.log(i);
}
// Output: 0, 1, 2, 4, 5, 6