Nested loop execution in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print numbers 1 to 3 using a for loop.

PHP

<?php
for ($i = 1; $i [1] 3; $i++) {
    echo $i . " ";
}
?>

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

A<=

B>=

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

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

The for loop should run while $i is less than or equal to 3 to print numbers 1, 2, and 3. Using <= will loop correctly.

2fill in blank

medium

Complete the code to print a 3x3 grid of stars using nested loops.

PHP

<?php
for ($i = 1; $i <= 3; $i++) {
    for ($j = 1; $j [1] 3; $j++) {
        echo "* ";
    }
    echo "<br>";
}
?>

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

A>=

B<

C>

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using < will print only 2 stars per line.

The inner loop should run while $j is less than or equal to 3 to print 3 stars per line.

3fill in blank

hard

Fix the error in the nested loop to print numbers 1 to 3 in each row.

PHP

<?php
for ($i = 1; $i <= 3; $i++) {
    for ($j = 1; $j [1] 3; $j++) {
        echo $j . " ";
    }
    echo "<br>";
}
?>

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

A<

B<=

C>

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using < will miss printing the number 3.

The inner loop must run while $j is less than or equal to 3 to print numbers 1, 2, and 3.

4fill in blank

hard

Fill both blanks to create a nested loop that prints a 4x4 grid of numbers.

PHP

<?php
for ($i = 1; $i [1] 4; $i++) {
    for ($j = 1; $j [2] 4; $j++) {
        echo $j . " ";
    }
    echo "<br>";
}
?>

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

A<=

B<

C>

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using < will print only 3 rows or columns.

Both loops should run while their counters are less than or equal to 4 to print numbers 1 to 4 in each row and 4 rows total.

5fill in blank

hard

Fill all three blanks to create a nested loop that prints a multiplication table from 1 to 3.

PHP

<?php
for ($i = 1; $i [1] 3; $i++) {
    for ($j = 1; $j [2] 3; $j++) {
        echo $i [3] $j . " ";
    }
    echo "<br>";
}
?>

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

A<=

B<

C*

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using < will miss the last row or column.

Using + instead of * will add numbers instead of multiplying.

Both loops run while their counters are less than or equal to 3. The multiplication operator (*) is used to print the product of $i and $j.

Practice

1. What happens when a nested loop runs in PHP?
for ($i = 0; $i < 2; $i++) {
for ($j = 0; $j < 3; $j++) {
// code
}
}

easy

A. The inner loop runs completely for each iteration of the outer loop.

B. The outer loop runs completely for each iteration of the inner loop.

C. Both loops run only once.

D. The loops run simultaneously without nesting.

Solution

1. Step 1: Understand loop nesting order

   The outer loop runs from 0 to 1 (2 times). For each outer loop iteration, the inner loop runs fully.

2. Step 2: Inner loop completes all cycles per outer iteration

   For each $i, $j runs from 0 to 2 (3 times), completing all inner cycles before next outer iteration.

3. Final Answer:

   The inner loop runs completely for each iteration of the outer loop. -> Option A

4. Quick Check:

   Inner loop finishes fully inside outer loop [OK]

Hint: Inner loop runs fully inside each outer loop cycle [OK]

Common Mistakes:

• Thinking outer loop runs inside inner loop
• Assuming loops run only once
• Confusing simultaneous execution

2. Which of the following is the correct syntax for a nested for loop in PHP?

easy

A. for ($i = 0; $i < 2; $i++) { for $j = 0; $j < 3; $j++ { echo $i . $j; } }

B. for ($i = 0; $i < 2; $i++) { for ($j = 0; $j < 3; $j++) { echo $i . $j; } }

C. for ($i = 0; $i < 2; $i++) for ($j = 0; $j < 3; $j++) echo $i . $j;

D. for $i = 0; $i < 2; $i++ { for $j = 0; $j < 3; $j++ { echo $i . $j; } }

Solution

1. Step 1: Check PHP for loop syntax

   PHP requires parentheses around loop conditions and braces for blocks.

2. Step 2: Validate nested loop syntax

   for ($i = 0; $i < 2; $i++) { for ($j = 0; $j < 3; $j++) { echo $i . $j; } } uses correct parentheses and braces for both loops and echo statement inside.

3. Final Answer:

   for ($i = 0; $i < 2; $i++) { for ($j = 0; $j < 3; $j++) { echo $i . $j; } } -> Option B

4. Quick Check:

   Correct parentheses and braces in nested loops [OK]

Hint: Use parentheses and braces properly in PHP loops [OK]

Common Mistakes:

• Omitting parentheses around loop conditions
• Missing braces for loop blocks
• Incorrect for loop syntax without $ sign

3. What is the output of this PHP code?

for ($i = 1; $i <= 2; $i++) {
  for ($j = 1; $j <= 3; $j++) {
    echo $i * $j . ' ';
  }
}

medium

A. 1 2 3 1 2 3

B. 1 4 9 2 5 8

C. 1 2 3 2 4 6

D. 6 12 18 6 12 18

Solution

1. Step 1: Trace outer loop values

   $i runs from 1 to 2.

2. Step 2: Trace inner loop and calculate products

   For $i=1: $j=1,2,3 -> 1*1=1, 1*2=2, 1*3=3
   For $i=2: $j=1,2,3 -> 2*1=2, 2*2=4, 2*3=6

3. Final Answer:

   1 2 3 2 4 6 -> Option C

4. Quick Check:

   Multiply outer and inner loop counters [OK]

Hint: Multiply outer and inner counters for output [OK]

Common Mistakes:

• Mixing up loop variable values
• Printing inner loop values only
• Ignoring multiplication in echo

4. Find the error in this nested loop PHP code:

for ($i = 0; $i < 3; $i++) {
  for ($j = 0; $j < 2; $i++) {
    echo $i . $j . ' ';
  }
}

medium

A. Inner loop increments $i instead of $j causing infinite loop.

B. Outer loop condition is incorrect.

C. Missing semicolon after echo statement.

D. Variables $i and $j are not declared.

Solution

1. Step 1: Check inner loop increment variable

   The inner loop increments $i instead of $j, which is wrong.

2. Step 2: Understand effect of wrong increment

   Incrementing $i inside inner loop changes outer loop variable unexpectedly, causing infinite or wrong behavior.

3. Final Answer:

   Inner loop increments $i instead of $j causing infinite loop. -> Option A

4. Quick Check:

   Increment correct loop variable to avoid errors [OK]

Hint: Increment inner loop variable inside inner loop [OK]

Common Mistakes:

• Incrementing wrong variable in inner loop
• Confusing loop conditions
• Assuming variables need declaration in PHP

5. You want to print a multiplication table from 1 to 3 using nested loops in PHP. Which code correctly prints the table with each row on a new line?

?

hard

A. for ($i = 1; $i <= 3; $i++) { for ($j = 1; $j <= 3; $j++) { echo $i * $j; } echo "\n"; }

B. for ($i = 1; $i <= 3; $i++) { for ($j = 1; $j <= 3; $j++) { echo $i * $j . "\n"; } }

C. for ($i = 1; $i <= 3; $i++) { for ($j = 1; $j <= 3; $j++) { echo $i * $j . ' '; } }

D. for ($i = 1; $i <= 3; $i++) { for ($j = 1; $j <= 3; $j++) { echo $i * $j . ' '; } echo "\n"; }

Solution

1. Step 1: Understand output format

   Each row should print products separated by spaces, then a newline after inner loop ends.

2. Step 2: Check each option for correct newline placement

   for ($i = 1; $i <= 3; $i++) { for ($j = 1; $j <= 3; $j++) { echo $i * $j . ' '; } echo "\n"; } prints products with spaces inside inner loop, then newline after inner loop completes, correctly formatting rows.

3. Final Answer:

   for ($i = 1; $i <= 3; $i++) { for ($j = 1; $j <= 3; $j++) { echo $i * $j . ' '; } echo "\n"; } -> Option D

4. Quick Check:

   Newline after inner loop completes for each row [OK]

Hint: Print newline after inner loop to separate rows [OK]

Common Mistakes:

• Printing newline inside inner loop
• Missing spaces between numbers
• No newline causing all output in one line