While loop execution flow in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple while loop

What is the output of the following Java code?

Java

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

A 1 2

B 1 2 3 4

C 0 1 2 3

D 1 2 3

💡 Hint

Remember the loop runs while the condition is true and increments i each time.

The loop starts with i=1 and runs while i is less than or equal to 3. It prints i and then increments it. So it prints 1, 2, and 3 with spaces.

❓ Predict Output

intermediate

While loop with break statement

What will be printed by this Java code?

Java

int i = 0;
while (i < 5) {
    if (i == 3) {
        break;
    }
    System.out.print(i + " ");
    i++;
}

A 0 1 2

B 0 1 2 3

C 1 2 3

D 0 1 2 3 4

💡 Hint

The break stops the loop when i equals 3.

The loop prints i starting from 0. When i reaches 3, the break stops the loop before printing 3. So output is 0 1 2

❓ Predict Output

advanced

While loop with continue statement

What is the output of this Java code snippet?

Java

int i = 0;
while (i < 5) {
    i++;
    if (i == 3) {
        continue;
    }
    System.out.print(i + " ");
}

A 1 2 3 4 5

B 0 1 2 4 5

C 1 2 4 5

D 1 2 3 5

💡 Hint

The continue skips printing when i is 3.

The loop increments i first. When i is 3, continue skips the print statement. So it prints 1, 2, 4, 5 with spaces.

🧠 Conceptual

advanced

Understanding while loop condition evaluation

Consider this code: int i = 5; while (i > 0) { System.out.print(i + " "); i -= 2; } How many times does the loop run?

A 2 times

B 3 times

C 4 times

D 5 times

💡 Hint

Count how i changes each loop and when the condition fails.

i starts at 5, then becomes 3, then 1, then -1 which stops the loop. So it runs 3 times.

❓ Predict Output

expert

While loop with nested conditions and variable changes

What is the output of this Java code?

Java

int i = 1;
int sum = 0;
while (i <= 5) {
    if (i % 2 == 0) {
        i++;
        continue;
    }
    sum += i;
    i++;
}
System.out.println(sum);

A 9

B 15

C 6

D 10

💡 Hint

Only odd numbers are added to sum because even numbers skip the addition.

The loop adds 1, 3, and 5 to sum. Even numbers 2 and 4 are skipped. So sum = 1+3+5 = 9.

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