For loop syntax in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print numbers from 1 to 5 using a for loop.

Java

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

Drag options to blanks, or click blank then click option'

A<=

B<

C>

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'i < 5' will stop the loop before printing 5.

Using 'i > 5' or 'i >= 5' will not run the loop as expected.

The for loop should run while i is less than or equal to 5 to print numbers 1 through 5.

2fill in blank

medium

Complete the code to sum numbers from 1 to 10 using a for loop.

Java

int sum = 0;
for (int num = 1; num [1] 10; num++) {
    sum += num;
}
System.out.println(sum);

Drag options to blanks, or click blank then click option'

A<=

B>=

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'num < 10' will exclude 10 from the sum.

Using 'num > 10' will not run the loop.

The loop must include 10, so the condition should be 'num <= 10'.

3fill in blank

hard

Fix the error in the for loop that counts down from 5 to 1.

Java

for (int i = 5; i [1] 1; i--) {
    System.out.println(i);
}

Drag options to blanks, or click blank then click option'

A>

B<=

C<

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' will stop the loop before printing 1.

Using '<' or '<=' will not run the loop correctly when counting down.

When counting down, the loop should continue while i is greater than or equal to 1 to print numbers from 5 down to 1.

4fill in blank

hard

Fill both blanks to create a for loop that prints even numbers from 2 to 10.

Java

for (int i = [1]; i [2] 10; i += 2) {
    System.out.println(i);
}

Drag options to blanks, or click blank then click option'

A2

B<

C<=

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Starting at 1 will print odd numbers.

Using '<' will exclude 10 from being printed.

The loop starts at 2 and runs while i is less than or equal to 10 to print even numbers up to 10.

5fill in blank

hard

Fill all three blanks to create a for loop that prints the squares of numbers from 1 to 5.

Java

for (int [1] = 1; [2] [3] 5; [1]++) {
    System.out.println([1] * [1]);
}

Drag options to blanks, or click blank then click option'

Ai

C<=

Dj

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in initialization and condition causes errors.

Using '<' excludes the last number 5.

The variable i is used for counting from 1 to 5 inclusive, printing squares.

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