While 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 while loop.

Java

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

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

A<=

B<

C>

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'i < 5' which stops before printing 5.

Using 'i > 5' which never runs the loop.

The condition i <= 5 ensures the loop runs while i is 1 through 5.

2fill in blank

medium

Complete the code to stop the loop when the variable count reaches 10.

Java

int count = 0;
while (count [1] 10) {
    System.out.println(count);
    count++;
}

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

A>

B<=

C>=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>=' which causes the loop to never run.

Using '<=' which runs the loop one extra time.

The loop should run while count is less than 10, so count < 10 is correct.

3fill in blank

hard

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

Java

int x = 5;
while (x [1] 0) {
    System.out.println(x);
    x--;
}

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

A>=

B<

C>

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' causes the loop to never run.

Using '>' alone excludes zero and may cause logic errors.

The condition x >= 0 ensures the loop runs while x is 5 down to 0, avoiding infinite loop.

4fill in blank

hard

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

Java

int num = 2;
while (num [1] 10) {
    System.out.println(num);
    num [2] 2;
}

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

A<=

B+=

C-=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' excludes 10 from output.

Using '-=' decreases num causing infinite loop.

The condition num <= 10 includes 10, and num += 2 increases num by 2 each time.

5fill in blank

hard

Fill all three blanks to create a while loop that counts down from 15 to 5 by 2.

Java

int val = [1];
while (val [2] [3]) {
    System.out.println(val);
    val -= 2;
}

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

A15

B>=

C5

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' instead of '>=' causes the loop to never run.

Starting at 5 instead of 15 prints wrong numbers.

Start at 15, loop while val is greater than or equal to 5, counting down by 2.

Practice

1. What does a while loop do in Java?

easy

A. Stops the program immediately

B. Executes code only once regardless of condition

C. Runs code only if a condition is false

D. Repeats a block of code as long as a condition is true

Solution

1. Step 1: Understand the purpose of a while loop

   A while loop repeats its code block while the condition remains true.

2. Step 2: Compare options with this behavior

   Only Repeats a block of code as long as a condition is true correctly describes this repeating behavior based on a true condition.

3. Final Answer:

   Repeats a block of code as long as a condition is true -> Option D

4. Quick Check:

   while loop repeats while condition true = A [OK]

Hint: Remember: while loops run only when condition is true [OK]

Common Mistakes:

• Thinking while loop runs once regardless of condition
• Confusing while with if statement
• Believing while loop runs when condition is false

2. Which of the following is the correct syntax to start a while loop in Java?

easy

A. while condition { }

B. while (condition) { }

C. while condition: { }

D. while (condition);

Solution

1. Step 1: Recall Java while loop syntax

   Java requires parentheses around the condition and curly braces for the loop body.

2. Step 2: Check each option

   while (condition) { } matches the correct syntax: while (condition) { }.

3. Final Answer:

   while (condition) { } -> Option B

4. Quick Check:

   Parentheses and braces needed = A [OK]

Hint: Use parentheses for condition and braces for loop body [OK]

Common Mistakes:

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

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

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

medium

A. Infinite loop

B. 1 2 3 4

C. 1 2 3

D. 0 1 2 3

Solution

1. Step 1: Analyze the loop condition and variable changes

   Variable i starts at 1 and increases by 1 each loop until i > 3.

2. Step 2: Trace the output for each iteration

   i=1 prints "1 ", i=2 prints "2 ", i=3 prints "3 ". Loop stops after i=4.

3. Final Answer:

   1 2 3 -> Option C

4. Quick Check:

   Prints 1 to 3 with spaces = D [OK]

Hint: Check loop start, end condition, and increments carefully [OK]

Common Mistakes:

• Forgetting i++ causes infinite loop
• Printing extra number after loop ends
• Starting i from 0 instead of 1

4. Identify the error in this code snippet:

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

medium

A. No update to count inside the loop causing infinite loop

B. Missing semicolon after while condition

C. Variable count is not initialized

D. Incorrect print statement syntax

Solution

1. Step 1: Check loop condition and variable updates

   The loop condition is count > 0, but count is never changed inside the loop.

2. Step 2: Understand effect of no update

   Without changing count, the loop runs forever, causing an infinite loop.

3. Final Answer:

   No update to count inside the loop causing infinite loop -> Option A

4. Quick Check:

   Loop variable must change to stop loop = B [OK]

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

Common Mistakes:

• Assuming loop stops without variable update
• Confusing syntax errors with logic errors
• Ignoring infinite loop risks

5. How many times will the loop run in this code?

int x = 10;
while (x > 0) {
  x -= 3;
  System.out.print(x + " ");
}

hard

A. 3 times

B. 5 times

C. 4 times

D. Infinite times

Solution

1. Step 1: Trace the value of x each iteration

   Start x=10. After each loop: x=7, x=4, x=1, x=-2 (loop stops after this).

2. Step 2: Count how many times loop runs

   Loop runs while x > 0, so it runs 3 times before x becomes -2.

3. Final Answer:

   3 times -> Option A

4. Quick Check:

   Subtract 3 until x ≤ 0 = 3 times [OK]

Hint: Count iterations by subtracting until condition fails [OK]

Common Mistakes:

• Counting one less or more iteration
• Ignoring last iteration where x becomes negative
• Assuming infinite loop without checking condition