Control Flow

Control flow refers to the order in which statements are executed in a program. By default, programs execute statements sequentially, from top to bottom. However, programming languages provide constructs that allow you to alter this default flow, enabling more complex and dynamic behavior. These constructs include conditional statements and loops.

Conditional Statements

Conditional statements allow your program to make decisions based on whether certain conditions are true or false. The most common conditional statement is the if statement.

The if Statement

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


if (condition) {
    // code to execute if condition is true
}

The if...else Statement

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


if (condition) {
    // code to execute if condition is true
} else {
    // code to execute if condition is false
}

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

This structure allows you to check multiple conditions in sequence. The first condition that evaluates to true will have its corresponding code block executed.


if (condition1) {
    // code to execute if condition1 is true
} else if (condition2) {
    // code to execute if condition2 is true
} else {
    // code to execute if no conditions are true
}

The switch Statement

The switch statement is a more concise way to select one of many code blocks to be executed. It's particularly useful when you have a single variable or expression to check against multiple possible constant values.

Example: Using switch


let day = "Monday";
switch (day) {
    case "Monday":
        console.log("It's the start of the week.");
        break;
    case "Friday":
        console.log("It's almost the weekend!");
        break;
    default:
        console.log("Just another day.");
}

The break statement is crucial in a switch statement; it prevents the execution from falling through to the next case.

Loops

Loops allow you to execute a block of code repeatedly. This is essential for processing collections of data or performing repetitive tasks.

The for Loop

The for loop is typically used when you know in advance how many times you want to iterate.


for (initialization; condition; afterthought) {
    // code to execute in each iteration
}

Initialization: Executed once before the loop starts (e.g., setting a counter to 0).

Condition: Evaluated before each iteration. If true, the loop continues; if false, the loop terminates.

Afterthought: Executed at the end of each iteration (e.g., incrementing the counter).

The while Loop

The while loop executes a block of code as long as a specified condition is true. The condition is checked at the beginning of each iteration.


while (condition) {
    // code to execute as long as condition is true
    // make sure to update variables that affect the condition to avoid infinite loops
}

The do...while Loop

The do...while loop is similar to the while loop, but it executes the code block *at least once* before checking the condition. This means the code inside the do block will always run, even if the condition is initially false.


do {
    // code to execute at least once
    // then check condition
} while (condition);
Important Note: Be careful with loops to avoid creating infinite loops. An infinite loop occurs when the condition controlling the loop never becomes false, causing the program to run indefinitely. Ensure that the variables involved in your loop conditions are updated correctly within the loop body.

Loop Control Statements

You can also use special statements to alter the behavior of loops: