Why loops are needed in Java - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a loop printing numbers

What is the output of this Java code that uses a loop to print numbers from 1 to 3?

Java

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

A 1 2 3

B 123

C 0 1 2 3

D 1 2 3 4

💡 Hint

Look at the loop start and end conditions carefully.

The loop starts at 1 and runs while i is less than or equal to 3, printing each number followed by a space.

🧠 Conceptual

intermediate

Why use loops instead of repeating code?

Why do programmers use loops instead of writing the same code multiple times?

A Loops reduce repeated code and make programs shorter and easier to maintain.

B Loops make programs run slower but look nicer.

C Loops are only used to confuse beginners.

D Loops are required to write any Java program.

💡 Hint

Think about what happens if you want to change repeated code.

Loops help avoid repeating the same lines many times, so if you need to change something, you only change it once inside the loop.

❓ Predict Output

advanced

Output of nested loops

What is the output of this nested loop code?

Java

for (int i = 1; i <= 2; i++) {
    for (int j = 1; j <= 2; j++) {
        System.out.print(i * j + " ");
    }
}

A 1 1 2 2

B 2 4 2 4

C 1 2 3 4

D 1 2 2 4

💡 Hint

Multiply i and j for each pair in the loops.

The outer loop runs i=1 and i=2. For each i, inner loop runs j=1 and j=2. Multiplying gives 1*1=1, 1*2=2, 2*1=2, 2*2=4.

🔧 Debug

advanced

Identify the error in this loop

What error does this code cause?

Java

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

A Compilation error: missing braces for loop body

B Runtime error: infinite loop

C No error, prints numbers 0 to 4

D Compilation error: variable i cannot be used outside the loop

💡 Hint

Check where variable i is used and declared.

The code increments i twice per loop iteration, but this is allowed and i is in scope. The code prints 0, 2, 4.

🚀 Application

expert

How many times does this loop run?

How many times will the loop body execute in this code?

Java

int count = 0;
for (int i = 10; i > 0; i -= 3) {
    count++;
}
System.out.println(count);

A 5

B 4

C 3

D 6

💡 Hint

Count how many times i stays greater than 0 when subtracting 3 each time.

i starts at 10, then 7, then 4, then 1, then -2 (loop stops). So loop runs 4 times.