Loop execution flow 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 '<' will stop the loop before printing 5.

Using '>' or '>=' will cause the loop not to run as expected.

The 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 while loop.

Java

int sum = 0;
int num = 1;
while(num [1] 10) {
    sum += num;
    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 '<' excludes 10 from the sum.

Using '>' or '>=' will cause the loop not to run properly.

The loop should continue while num is less than or equal to 10 to include 10 in the sum.

3fill in blank

hard

Fix the error in the for loop condition to avoid an infinite loop.

Java

for(int i = 0; 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--' with 'i < 5' causes an infinite loop.

Using '>' with 'i--' is correct but not matching the current code.

The loop should increment i and run while i is less than 5 to avoid infinite loop.

4fill in blank

hard

Fill both blanks to create a 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

B1

C<=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Starting at 1 will print odd numbers.

Using '<' will exclude 10 from printing.

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 loop that prints numbers from 10 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'

A1

B>=

C--

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' with decrement causes the loop not to run.

Using '++' instead of '--' will cause an infinite loop.

The loop starts at 10, runs while i is greater than or equal to 1, and decrements i by 1 each time.

Practice

1. What does a for loop in Java primarily do?

easy

A. Executes code only once

B. Stops the program immediately

C. Repeats a block of code a specific number of times

D. Creates a new variable

Solution

1. Step 1: Understand the purpose of a for loop and compare options

   A for loop is designed to repeat a block of code multiple times based on a condition. Only "Repeats a block of code a specific number of times" correctly describes it.

2. Final Answer:

   Repeats a block of code a specific number of times -> Option C

3. Quick Check:

   for loop = repeat code [OK]

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

Common Mistakes:

• Thinking for loops run only once
• Confusing loops with variable declarations
• Believing loops stop the program

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

easy

A. while (condition); { // code }

B. while condition { // code }

C. while: (condition) { // code }

D. while (condition) { // code }

Solution

1. Step 1: Recall Java while loop syntax and check options

   The correct syntax requires parentheses around the condition and braces for the code block. Only "while (condition) { // code }" matches: while (condition) { // code }.

2. Final Answer:

   while (condition) { // code } -> Option D

3. Quick Check:

   while loop syntax = parentheses + braces [OK]

Hint: While loops need parentheses and braces [OK]

Common Mistakes:

• Omitting parentheses around condition
• Adding semicolon after while condition
• Using colon instead of parentheses

3. What will be the output of this Java code?

int count = 0;
while (count < 3) {
  System.out.print(count + " ");
  count++;
}

medium

A. 0 1 2

B. 1 2 3

C. 0 1 2 3

D. 3 2 1

Solution

1. Step 1: Analyze the loop condition and trace iterations

   The loop runs while count is less than 3, starting from 0. It prints 0, then increments to 1; prints 1, increments to 2; prints 2, increments to 3; then stops because 3 is not less than 3.

2. Final Answer:

   0 1 2 -> Option A

3. Quick Check:

   Prints 0,1,2 then stops [OK]

Hint: Count starts at 0 and stops before 3 [OK]

Common Mistakes:

• Including 3 in output
• Starting count from 1
• Printing in reverse order

4. Identify the error in this loop code:

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

medium

A. Missing increment of i inside the loop

B. Incorrect loop condition syntax

C. Missing semicolon after while

D. Variable i should be declared inside the loop

Solution

1. Step 1: Check loop control variable and consequences

   The variable i is initialized but never changed inside the loop. Without incrementing i, the condition i < 5 is always true, causing an infinite loop.

2. Final Answer:

   Missing increment of i inside the loop -> Option A

3. Quick Check:

   Loop needs variable update to stop [OK]

Hint: Always update loop variable to avoid infinite loops [OK]

Common Mistakes:

• Forgetting to increment loop variable
• Misplacing semicolons
• Declaring variable inside loop unnecessarily

5. Consider this code snippet:

int sum = 0;
for (int i = 1; i <= 5; i++) {
  if (i == 3) continue;
  sum += i;
}
System.out.println(sum);

What is the output and why?

hard

A. 15 because all numbers 1 to 5 are added

B. 12 because number 3 is skipped in addition

C. 10 because only numbers less than 3 are added

D. Error due to incorrect use of continue

Solution

1. Step 1: Trace the loop and effect of continue

   The loop runs from 1 to 5. When i equals 3, continue skips the addition for that iteration. Sum = 1 + 2 + 4 + 5 = 12 because 3 is skipped.

2. Final Answer:

   12 because number 3 is skipped in addition -> Option B

3. Quick Check:

   continue skips 3, sum = 12 [OK]

Hint: Continue skips current loop iteration [OK]

Common Mistakes:

• Adding 3 despite continue
• Thinking continue causes error
• Summing only numbers less than 3