Why loops are needed in Java - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

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

Java

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

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

A10

B1

C5

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 10 instead of 5 makes the loop run too many times.

Using 0 will not print any numbers because i starts at 1.

The loop should run from 1 to 5, so the condition uses 5.

2fill in blank

medium

Complete the code to sum numbers from 1 to 4 using a loop.

Java

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

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

A4

B3

C5

D6

Attempts:

3 left

💡 Hint

Common Mistakes

Using 5 will add an extra number.

Using 3 will miss the number 4.

The loop should add numbers from 1 to 4, so the condition uses 4.

3fill in blank

hard

Fix the error in the loop condition to print numbers from 0 to 3.

Java

for(int i = 0; i [1] 3; 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 before printing 3.

Using == will only run once when i is 3.

The loop should include 3, so use <= to include it.

4fill in blank

hard

Fill both blanks to create a loop that prints even numbers from 2 to 6.

Java

for(int i = [1]; i [2] 6; 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 miss printing 6.

The loop starts at 2 and runs while i is less than or equal to 6 to include 6.

5fill in blank

hard

Fill all three blanks to create a loop that prints numbers from 5 down to 1.

Java

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

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

A5

B>=

C--

D++

Attempts:

3 left

💡 Hint

Common Mistakes

Using ++ will increase i and cause an infinite loop.

Using <= will never run because 5 is not less than or equal to 1.

The loop starts at 5, runs while i is greater than or equal to 1, and decreases i by 1 each time.

Practice

1.

Why do we use loops in Java programming?

easy

A. To repeat a block of code multiple times without rewriting it

B. To store multiple values in a single variable

C. To create new data types

D. To stop the program from running

Solution

1. Step 1: Understand the purpose of loops

   Loops allow repeating the same code multiple times without writing it again and again.

2. Step 2: Compare with other options

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

3. Final Answer:

   To repeat a block of code multiple times without rewriting it -> Option A

4. Quick Check:

   Loops repeat code = C [OK]

Hint: Loops repeat code to avoid rewriting [OK]

Common Mistakes:

• Confusing loops with variables
• Thinking loops create new data types
• Believing loops stop program execution

2.

Which of the following is the correct syntax for a for loop in Java that runs 5 times?

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

easy

A. for (int i = 1; i <= 5; i--) { ... }

B. for i = 0 to 5 { ... }

C. loop (int i = 0; i < 5; i++) { ... }

D. for (int i = 0; i < 5; i++) { ... }

Solution

1. Step 1: Check Java for loop syntax

   The correct syntax uses: for (initialization; condition; update) { ... }

2. Step 2: Validate each option

   for (int i = 0; i < 5; i++) { ... } matches correct syntax. B and C use invalid keywords. D has wrong update (i-- decreases).

3. Final Answer:

   for (int i = 0; i < 5; i++) { ... } -> Option D

4. Quick Check:

   Java for loop syntax = A [OK]

Hint: Remember for loop: init; condition; increment [OK]

Common Mistakes:

• Using 'to' instead of semicolons
• Wrong loop variable update (i-- instead of i++)
• Using non-Java keywords like 'loop'

3.

What will be the output of this 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 loop range

   The loop starts at i=1 and runs while i <= 3, so i takes values 1, 2, 3.

2. Step 2: Determine printed output

   Each iteration prints 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 = B [OK]

Hint: Check loop start and end values carefully [OK]

Common Mistakes:

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

4.

Find the error in this Java loop code:

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

medium

A. Missing semicolon after the for statement

B. The loop variable 'i' should start at 5

C. The loop variable 'i' is decreasing, causing an infinite loop

D. The print statement is incorrect

Solution

1. Step 1: Check loop update expression

   The loop decreases i (i--) but condition is i < 5, so i moves away from stopping condition.

2. Step 2: Understand loop behavior

   Since i starts at 0 and decreases, i will always be less than 5, causing infinite loop.

3. Final Answer:

   The loop variable 'i' is decreasing, causing an infinite loop -> Option C

4. Quick Check:

   Decreasing i with i < 5 causes infinite loop = A [OK]

Hint: Check if loop variable moves toward stopping condition [OK]

Common Mistakes:

• Confusing i-- with i++
• Ignoring loop condition logic
• Assuming print statement causes error

5.

You want to print all even numbers from 2 to 10 using a loop. Which code snippet correctly uses a for loop to do this?

hard

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

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

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

D. for (int i = 10; i >= 2; i--) { if (i % 2 == 0) System.out.print(i + " "); }

Solution

1. Step 1: Understand the goal

   We want to print even numbers from 2 to 10 in ascending order.

2. Step 2: Evaluate each option

   for (int i = 2; i <= 10; i += 2) { System.out.print(i + " "); } starts at 2, increments by 2, prints 2,4,6,8,10 correctly.
   for (int i = 1; i <= 10; i++) { if (i % 2 == 1) System.out.print(i + " "); } prints odd numbers 1 3 5 7 9 (incorrect).
   for (int i = 2; i < 10; i++) { System.out.print(i * 2 + " "); } prints multiples of 2 but stops at i=9, so last number is 18 (incorrect).
   for (int i = 10; i >= 2; i--) { if (i % 2 == 0) System.out.print(i + " "); } prints even numbers but in descending order (10 to 2).

3. Step 3: Choose best answer

   for (int i = 2; i <= 10; i += 2) { System.out.print(i + " "); } is simplest and matches requirement exactly.

4. Final Answer:

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

5. Quick Check:

   Increment by 2 from 2 to 10 = D [OK]

Hint: Use i += 2 to jump even numbers [OK]

Common Mistakes:

• Using wrong loop bounds
• Printing odd numbers by mistake
• Confusing ascending with descending order