For loop syntax in Java - Mini Project: Build & Apply

For loop syntax

📖 Scenario: You are organizing a small event and want to print the names of all the guests attending.

🎯 Goal: Write a Java program that uses a for loop to print each guest's name from a list.

📋 What You'll Learn

Create an array of guest names

Use a for loop with an index variable i

Print each guest name inside the loop

💡 Why This Matters

🌍 Real World

Printing lists of names or items is common in event planning, inventory management, and many other tasks.

💼 Career

Understanding for loops is essential for iterating over data structures in software development.

1

Create the guest list array

Create a String array called guests with these exact names: "Alice", "Bob", "Charlie".

Java

// Create the guests array with names "Alice", "Bob", "Charlie"
// Your code here

Hint

Use curly braces {} to list the names inside the array.

2

Add a loop counter variable

Inside the main method, create an integer variable called i and set it to 0 before the loop.

Java

public class Main {
    public static void main(String[] args) {
        String[] guests = {"Alice", "Bob", "Charlie"};
        // Create int variable i and set to 0
        // Your code here
    }
}

Hint

Declare int i = 0; before the loop starts.

3

Write the for loop to print guest names

Write a for loop using i starting at 0, running while i < guests.length, and incrementing i by 1 each time. Inside the loop, print guests[i].

Java

public class Main {
    public static void main(String[] args) {
        String[] guests = {"Alice", "Bob", "Charlie"};
        int i = 0;
        // Write for loop: for (i = 0; i < guests.length; i++)
        // Inside loop print guests[i]
        // Your code here
    }
}

Hint

Use for (i = 0; i < guests.length; i++) and inside the loop print guests[i].

4

Print the guest names

Run the program and print each guest name using System.out.println(guests[i]) inside the for loop.

Java

public class Main {
    public static void main(String[] args) {
        String[] guests = {"Alice", "Bob", "Charlie"};
        int i = 0;
        for (i = 0; i < guests.length; i++) {
            // Print guest name
            // Your code here
        }
    }
}

Hint

Make sure to print each name inside the loop using System.out.println(guests[i]).

Practice

1.

What is the main purpose of a for loop in Java?

easy

A. To define a new class

B. To make decisions based on conditions

C. To repeat a block of code a specific number of times

D. To store multiple values in a list

Solution

1. Step 1: Understand the role of a for loop

   A for loop is used to repeat code multiple times when the number of repetitions is known.

2. Step 2: Compare with other options

   Options A, B, and C describe other programming concepts, not loops.

3. Final Answer:

   To repeat a block of code a specific number of times -> Option C

4. Quick Check:

   For loop = repeat code fixed times [OK]

Hint: For loops repeat code a set number of times [OK]

Common Mistakes:

• Confusing for loop with if statement
• Thinking for loop stores data
• Mixing for loop with class definition

2.

Which of the following is the correct syntax for a basic for loop in Java?

for (int i = 0; i < 5; i++) {
    System.out.println(i);
}

easy

A. for (int i = 0; i < 5; i++) { System.out.println(i); }

B. for int i = 0; i < 5; i++ { System.out.println(i); }

C. for (int i = 0; i < 5; i++) System.out.println(i)

D. for (int i = 0; i < 5; i++) System.out.println(i); }

Solution

1. Step 1: Check the for loop syntax structure

   The correct syntax requires parentheses around initialization, condition, and increment, and braces to enclose the loop body.

2. Step 2: Validate each option

   for (int i = 0; i < 5; i++) { System.out.println(i); } has correct syntax with parentheses and braces. for int i = 0; i < 5; i++ { System.out.println(i); } misses parentheses. for (int i = 0; i < 5; i++) System.out.println(i) misses semicolon after println(i). for (int i = 0; i < 5; i++) System.out.println(i); } has an extra closing brace.

3. Final Answer:

   for (int i = 0; i < 5; i++) { System.out.println(i); } -> Option A

4. Quick Check:

   Correct for loop syntax = for (int i = 0; i < 5; i++) { System.out.println(i); } [OK]

Hint: For loop needs parentheses and braces for multiple statements [OK]

Common Mistakes:

• Omitting parentheses around loop control
• Missing braces for multiple statements
• Extra or missing braces

3.

What will be the output of the following Java code?

for (int i = 1; i <= 3; i++) {
    System.out.print(i + " ");
}

medium

A. 0 1 2

B. 1 2 3

C. 1 2 3 4

D. 3 2 1

Solution

1. Step 1: Analyze the loop range

   The loop starts at i=1 and runs while i is less than or equal to 3, so i takes values 1, 2, and 3.

2. Step 2: Determine the output

   Each iteration prints the current i followed by a space, so output is "1 2 3 "

3. Final Answer:

   1 2 3 -> Option B

4. Quick Check:

   Prints 1 to 3 with spaces = 1 2 3 [OK]

Hint: Check loop start, end, and print inside loop [OK]

Common Mistakes:

• Starting loop at 0 instead of 1
• Including extra number beyond 3
• Printing in reverse order

4.

Identify the error in the following for loop code snippet:

for (int i = 0; i < 5; i++)
    System.out.println(i);
}

medium

A. Extra closing brace } without matching opening brace

B. Incorrect loop condition syntax

C. Missing semicolon after i++

D. Variable i not declared

Solution

1. Step 1: Check loop syntax and braces

   The for loop has no opening brace but has a closing brace, which is unmatched and causes a syntax error.

2. Step 2: Verify other parts

   Semicolons and variable declaration are correct, and the loop condition syntax is valid.

3. Final Answer:

   Extra closing brace } -> Option A

4. Quick Check:

   Unmatched brace causes syntax error = Extra closing brace } without matching opening brace [OK]

Hint: Match every opening brace with a closing brace [OK]

Common Mistakes:

• Leaving unmatched braces
• Forgetting semicolons in loop header
• Not declaring loop variable

5.

How can you write a for loop in Java that prints only even numbers from 2 to 10 inclusive?

hard

A. for (int i = 0; i <= 10; i += 2) { System.out.print(i + " "); }

B. for (int i = 1; i < 10; i++) { if (i % 2 == 0) System.out.print(i + " "); }

C. for (int i = 2; i < 10; i++) { System.out.print(i * 2 + " "); }

D. for (int i = 2; i <= 10; i += 2) { System.out.print(i + " "); }

Solution

1. Step 1: Understand the requirement

   We want to print even numbers from 2 to 10 inclusive, so numbers: 2, 4, 6, 8, 10.

2. Step 2: Analyze each option

   for (int i = 2; i <= 10; i += 2) { System.out.print(i + " "); } starts at 2 and increments by 2 up to 10, printing even numbers correctly. for (int i = 1; i < 10; i++) { if (i % 2 == 0) System.out.print(i + " "); } uses a condition inside the loop but loops only up to 9, missing 10. for (int i = 2; i < 10; i++) { System.out.print(i * 2 + " "); } prints multiples of 2 starting at 4 (2*2), but loop ends before 10 and prints wrong numbers. for (int i = 0; i <= 10; i += 2) { System.out.print(i + " "); } starts at 0, which is not in the required range.

3. Final Answer:

   for (int i = 2; i <= 10; i += 2) { System.out.print(i + " "); } -> Option D

4. Quick Check:

   Increment by 2 from 2 to 10 = for (int i = 2; i <= 10; i += 2) { System.out.print(i + " "); } [OK]

Hint: Use i += 2 starting at 2 for even numbers [OK]

Common Mistakes:

• Starting loop at 0 instead of 2
• Using wrong loop condition
• Multiplying inside print instead of increment