JavaScript: Step 3- Control flow statements (if/else, switch/case, loops)

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Control flow statements help determine the order in which different parts of your code run. In JavaScript, you have if/else statements, switch/case statements, and various types of loops. They work similarly to Java’s control flow constructs.

1. If/Else Statements

These statements let you execute different blocks of code based on a condition. This is similar to Java’s if/else statements.

Syntax:

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

Example Program:

let x = 5;

if (x > 2) {
  console.log("x is greater than 2");
} else {
  console.log("x is less than or equal to 2");
}

Output:

x is greater than 2

Comparison to Java:

This is very similar to Java’s if statements:

int x = 5;

if (x > 2) {
    System.out.println("x is greater than 2");
} else {
    System.out.println("x is less than or equal to 2");
}

2. Switch/Case Statements

These are used to select one block of code to execute based on the value of an expression. It’s similar to Java’s switch statements.

Syntax:

switch (expression) {
  case value1:
    // code to execute if expression equals value1
    break;
  case value2:
    // code to execute if expression equals value2
    break;
  default:
    // code to execute if no cases match
}

Example Program:

let day = "Monday";

switch (day) {
  case "Monday":
    console.log("Today is Monday");
    break;
  case "Tuesday":
    console.log("Today is Tuesday");
    break;
  default:
    console.log("Today is neither Monday nor Tuesday");
}

Output:

Today is Monday

Comparison to Java:

This is similar to Java’s switch statement:

String day = "Monday";

switch (day) {
    case "Monday":
        System.out.println("Today is Monday");
        break;
    case "Tuesday":
        System.out.println("Today is Tuesday");
        break;
    default:
        System.out.println("Today is neither Monday nor Tuesday");
}

3. Loops

Loops let you repeat a block of code multiple times. JavaScript has for, while, and do/while loops, just like Java.

a. For Loop

Use this when you know how many times you need to loop.

Syntax:

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

Example Program:

for (let i = 1; i <= 5; i++) {
  console.log(i);
}

Output:

1
2
3
4
5

Comparison to Java:

Similar to Java’s for loop:

for (int i = 1; i <= 5; i++) {
    System.out.println(i);
}

b. While Loop

Use this when you don’t know how many times you need to loop but have a condition.

Syntax:

while (condition) {
  // code to execute in each iteration
}

Example Program:

let i = 1;

while (i <= 5) {
  console.log(i);
  i++;
}

Output:

1
2
3
4
5

Comparison to Java:

Similar to Java’s while loop:

int i = 1;

while (i <= 5) {
    System.out.println(i);
    i++;
}

c. Do/While Loop

This loop executes the block of code at least once, even if the condition is false.

Syntax:

do {
  // code to execute in each iteration
} while (condition);

Example Program:

let i = 1;

do {
  console.log(i);
  i++;
} while (i <= 5);

Output:

1
2
3
4
5

Comparison to Java:

Similar to Java’s do/while loop:

int i = 1;

do {
    System.out.println(i);
    i++;
} while (i <= 5);

Control flow statements are essential for making decisions and repeating actions in your programs. By understanding and using these statements effectively, you can create more complex and dynamic JavaScript programs.

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