Functions and Control Flow (If Statements, Loops)

What are Functions?
Functions are reusable blocks of code designed to perform a specific task. Functions help make code more organized, readable, and efficient by allowing you to reuse the same logic in different parts of your program.

How to Define a Function:
Functions are defined using the function keyword, followed by a name and parentheses ( ). Code inside the curly braces { } is the body of the function.

Syntax:

function functionName() {

 // Code to be executed 

}

Example:

function sayHello() {
   console.log("Hello, World!");
}
sayHello();  // Output: Hello, World!
 

Example:

function addNumbers(num1, num2) {
   return num1 + num2;
}
console.log(addNumbers(5, 10));  // Output: 15
 

Questions & Answers:

• Q: What is a function in JavaScript?
  • A: A function is a reusable block of code that performs a specific task.
• Q: How do you call a function named greet?
  • A: Use great( );

What is Control Flow?
Control flow determines the order in which your code executes. With if statements, you can execute different blocks of code depending on whether a condition is true or false.

Syntax for If Statements:

if (condition) {
   // Code to execute if the condition is true
}
 

Example:

let age = 18;
if (age >= 18) {
   console.log("You are eligible to vote.");
} else {
   console.log("You are not eligible to vote.");
}
Else If Statements:
To check multiple conditions, use else if.

Example:

let grade = 85;
if (grade >= 90) {
   console.log("You got an A!");
} else if (grade >= 80) {
   console.log("You got a B!");
} else {
   console.log("You need to study more.");
}

Questions & Answers:

• Q: What is an if statement used for?
  • A: It is used to execute code based on whether a condition is true or false.
• Q: How do you check multiple conditions?
  • A: Use else if statements for additional conditions.

What are Loops?
Loops allow you to repeat a block of code multiple times. There are several types of loops in JavaScript, but the most common are for loops and while loops.

Syntax:

for (initialization; condition; increment) {
   // Code to execute
}

Example:

for (let i = 0; i < 5; i++) {
   console.log("Counting: " + i);
}
// Output: Counting: 0, Counting: 1, ..., Counting: 4
 

Syntax:
while (condition) {
   // Code to execute
}
 

Example:

let i = 0;
while (i < 3) {
   console.log("Hello, World!");
   i++;
}
// Output: Hello, World! (3 times)
 

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

Example:

for (let i = 0; i < 5; i++) {
   if (i === 3) {
       break;  // Exit the loop when i is 3
   }
   console.log(i);  // Output: 0, 1, 2
}
 

Questions & Answers:

• Q: What is the difference between for and while loops?
  • A: A for loop runs for a specified number of iterations, while a while loop runs as long as its condition is true.
• Q: What does break do in a loop?
  • A: It exits the loop immediately, skipping any remaining iterations.

Example:
Let’s create a function to check if a number is even or odd using an if statement.

function checkEvenOdd(number) {
   if (number % 2 === 0) {
       return "Even";
   } else {
       return "Odd";
   }
}
console.log(checkEvenOdd(10));  // Output: Even
console.log(checkEvenOdd(7));   // Output: Odd
 

Objective:
Create a number guessing game where the user tries to guess a random number between 1 and 10.

Code Example:

function numberGuesser() {
   let randomNumber = Math.floor(Math.random() * 10) + 1;
   let guess;
   let attempts = 0;

   while (guess !== randomNumber) {
       guess = parseInt(prompt("Guess a number between 1 and 10: "));
       attempts++;
       if (guess < randomNumber) {
           console.log("Too low, try again.");
       } else if (guess > randomNumber) {
           console.log("Too high, try again.");
       } else {
           console.log(`Correct! You guessed it in ${attempts} attempts.`);
       }
   }
}
numberGuesser();
 

Questions for the Mini-Project:

• Q: What JavaScript method generates random numbers?
  • A: Math.random( ) generates a random decimal number between 0 and 1.
• Q: How do you convert a decimal number to an integer?
  • A: Use Math.floor( ) or Math.ceil( ).

Recap:

• Functions help organize and reuse code. You can pass inputs to functions and get outputs using parameters and return values.
• Control flow with if, else if, and else lets your code make decisions.
• Loops, such as for and while, allow you to execute repetitive tasks efficiently.

Next Steps:

• Practice writing your own functions and loops.
• In the next tutorial, we’ll explore arrays and objects, two essential data structures in JavaScript.