Java Programming · Week 4

Loops

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Java Guided Tutorials - Loops

What You'll Learn

Welcome to our Java Loops Tutorial! This lesson is all about understanding loop structures in Java. Loops are essential in programming as they allow your code to repeat a specific set of instructions multiple times without rewriting them. We'll go through different types of loops and understand how to apply them in various situations.

Lesson Breakdown:

For Loops: Used for repeating actions when you know the exact number of repetitions.
While Loops: Useful when you need to keep repeating until a condition is met, but you don't know how many repetitions are needed beforehand.
Do-While Loops: Similar to while loops but ensures at least one execution of the code block.
Weekly Project: Apply loops to create your own interactive program.

By the end of this lesson, you'll be able to decide which type of loop to use and implement loops to make your Java programs more powerful and efficient.

1. Introduction to For Loops in Java

For Loops

A for loop is ideal for repeating an action a specific number of times. For example, if you want to print numbers from 1 to 5, a for loop lets you set up a counter that automatically stops after reaching 5.

Here's the basic structure of a for loop:

for (initialization; condition; update) {
    // code to be repeated
}

Initialization: Set up your loop counter variable (often named i).
Condition: Define the stopping condition for the loop (e.g., i <= 5).
Update: Update the counter after each loop iteration (e.g., i++ to increase the counter).

Now, let's look at a simple example:

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

Try it Yourself

Complete the following program to use a for loop that prints numbers from 1 to 5.

Starter code

public class NumberPrinter {
    public static void main(String[] args) {
        // Use a for loop to print numbers from 1 to 5
    }
}

Write your code here

Make it print 1 2 3 4 5

Did it work?

Your program should print this:

Paste what you got:

2. Working with While Loops in Java

While Loops

A while loop is ideal when you need to repeat an action until a certain condition becomes false. Unlike a for loop, a while loop doesn't rely on a specific number of repetitions. Instead, it continues as long as its condition is true.

Here's the basic structure of a while loop:

while (condition) {
    // code to be repeated
}

For example, you could use a while loop to count down from 5 to 1:

int count = 5;
while (count > 0) {
    System.out.println(count);
    count--;
}

Try it Yourself

Complete the CountdownTimer program below. Use a while loop to count down from 5 to 1 and end with "Blastoff!"

Starter code

public class CountdownTimer {
    public static void main(String[] args) {
        int count = 5;

        // Use a while loop to count down from 5 to 1
        System.out.println("Blastoff!");
    }
}

Write your code here

Make it print 5 4 3 2 1 Blastoff!

Did it work?

Your program should print this:

5
4
3
2
1
Blastoff!

Paste what you got:

3. Understanding Do-While Loops in Java

Do-While Loops

A do-while loop is similar to a while loop but with one key difference: it guarantees that the loop will execute at least once before checking the condition. This makes it useful when you want a piece of code to run at least one time regardless of the condition.

Here's the basic structure of a do-while loop:

do {
    // code to be repeated
} while (condition);

For example, if you want a program to keep asking for a positive number until the user enters one, a do-while loop would work well:

import java.util.Scanner;

Scanner scanner = new Scanner(System.in);
int number;

do {
    System.out.println("Please enter a positive number: ");
    number = scanner.nextInt();
} while (number <= 0);

System.out.println("You entered: " + number);

Try it Yourself

Complete the PositiveNumberChecker program. Use a do-while loop to keep asking for a positive number until the user enters one.

Starter code

import java.util.Scanner;

public class PositiveNumberChecker {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int number;

        // Use a do-while loop to keep asking for a positive number

        scanner.close();
    }
}

Write your code here

Make it print Please enter a positive number: Please enter a positive number: You entered: 5

Did it work?

Your program should print this:

Please enter a positive number: 
Please enter a positive number: 
You entered: 5

Paste what you got:

4. Weekly Project: Number Guessing Game

Project Description

Create a Java program for a simple number guessing game. This project will incorporate all the loop concepts you've learned.

Requirements:

Generate a random number between 1 and 100
Use a loop to allow the user to guess multiple times
Provide feedback on whether the guess is too high or too low
Keep track of the number of guesses
End the game when the correct number is guessed

Implement the NumberGuessingGame program. Use the online compiler below to write and test your code. Once you're satisfied with your program, paste the output in the autograder to check your work.

Starter code

import java.util.Scanner;
import java.util.Random;

public class NumberGuessingGame {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        Random random = new Random();
        int numberToGuess = random.nextInt(100) + 1;
        int userGuess;
        int numberOfGuesses = 0;

        // Your code here
        // Implement the number guessing game using a loop

        scanner.close();
    }
}

Write your code here

Make it print Enter your guess: Too low! Try again. Enter your guess: Too high! Try again. Enter your guess: Congratulations! You guessed the number in 3 tries.

Did it work?

Your program should print this:

Enter your guess: 
Too low! Try again.
Enter your guess: 
Too high! Try again.
Enter your guess: 
Congratulations! You guessed the number in 3 tries.

Paste what you got:

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