PHP Mirror Number Pattern (0-Centered)

Beginner
5 min read
Updated: Sep 2026
3 programs
Live preview
0-centered descending mirror number pattern ending with 1234567890987654321 in PHP programming
Definition

What Is This Pattern?

A 0-centered descending mirror prints ascending digits $i..$max, a fixed 0, then descending $max..$i — each row mirrors around zero.

Remember
Rule: for i from max+1 down to 1
        print j from i to max
        print 0
        print k from max down to i

0
909
89098
7890987
678909876
56789098765
4567890987654
345678909876543
23456789098765432
1234567890987654321     ← max = 9

Follows the palindrome triangle in Program 27; next is the spaced mirror in Program 29.

Approach

How to Solve It

Outer loop decreases $i from $max + 1 to 1. Print left half, then 0, then the mirror half.

MethodIdeaBest for
Three loops + fixed 0Ascend $i..$max, print 0, descend $max..$iLearning, interviews, exams
Spaced digitsSame loops with echo $j . " "Easier reading for larger max

Pseudocode

Pseudocode
for i from max + 1 down to 1:
    for j from i to max:
        print j
    print 0
    for k from max down to i:
        print k
    print newline

Cheat sheet

GoalPattern
Shrink start digitfor ($i = $max + 1; $i >= 1; $i--)
Left ascendingfor ($j = $i; $j <= $max; $j++) echo $j;
Fixed centerecho "0";
Right mirrorfor ($k = $max; $k >= $i; $k--) echo $k;
End of rowecho PHP_EOL;

Printing Numbers vs Starting a New Line

APIEffectUse for
echo $j / $k / "0"Stays on the same lineEach digit on the row
echo PHP_EOLEnds the current lineAfter both half-loops and the center finish

Print digits without a newline, then end the row once.

Try it

Live Preview

Change the max digit and the 0-centered mirror updates instantly — capped at 9 for readable demos.

Whole numbers from 1 to 9. Tap a chip or type a value — the preview redraws as you go.

Live result max = 5 · 36 digits
0
505
45054
3450543
234505432
12345054321
Trace

Worked Walkthrough — $max = 4

Trace how left half, center 0, and right half build each row as $i decreases.

$iLeftCenterRightPrints
5(none)0(none)0
4404404
33404334043
223404322340432
1123404321123404321

There are $max + 1 rows. Digit total = (max + 1)² → O(n²) for max digit n.

Code

PHP Programs

Three complete programs: fixed $max = 9, CLI input, and a compact $max = 3 demo. Use View Output to reveal sample results.

Example 1 — Fixed $max = 9

Hard-coded max digit — ascend $i..9, print 0, then mirror 9..$i.

PHP
<?php
for ($i = 10; $i >= 1; $i--) {
    for ($j = $i; $j < 10; $j++) {
        echo $j;
    }

    echo "0";

    for ($k = 9; $k >= $i; $k--) {
        echo $k;
    }

    echo PHP_EOL;
}
?>

How It Works

1. Outer shrinks the start. $i runs from 10 down to 1 so each row grows.

2. Left, center, right. Print $i..9, then 0, then 9..$i on the same line.

3. First row is just 0. When $i = 10, both half-loops are empty — only the center prints.

Example 2 — User Input Max

Read $max from the CLI, validate, then use the same three-part core.

PHP
<?php
echo "Enter max digit (1-9): ";
$input = trim(fgets(STDIN));

if (!is_numeric($input) || (int) $input < 1 || (int) $input > 9) {
    echo "Please enter a whole number from 1 to 9." . PHP_EOL;
    exit(1);
}

$max = (int) $input;

for ($i = $max + 1; $i >= 1; $i--) {
    for ($j = $i; $j <= $max; $j++) {
        echo $j;
    }

    echo "0";

    for ($k = $max; $k >= $i; $k--) {
        echo $k;
    }

    echo PHP_EOL;
}
?>

How It Works

1. Prompt and validate. Reject non-numeric values and anything outside 1..9 before printing.

2. Same core. Replace hard-coded 9 / 10 with $max / $max + 1.

3. Safer input tip. Keep demos readable by capping at single digits:

Safer input
if (!is_numeric($input) || (int) $input < 1 || (int) $input > 9) {
    echo "Enter a whole number from 1 to 9." . PHP_EOL;
    exit(1);
}

Example 3 — Compact $max = 3

Same structure with a small max — easy to confirm the empty first row and growing halves.

PHP
<?php
$max = 3;

for ($i = $max + 1; $i >= 1; $i--) {
    for ($j = $i; $j <= $max; $j++) {
        echo $j;
    }

    echo "0";

    for ($k = $max; $k >= $i; $k--) {
        echo $k;
    }

    echo PHP_EOL;
}
?>

How It Works

1. Four rows. $i = 4 → 0; $i = 3 → 303; then 23032 and 1230321.

2. Trace on paper. If you forget echo "0", the halves glue together with no center.

3. Scale up next. Once the small demo is clear, use Examples 1–2 for max 9 or user input.

Edge Cases & Pitfalls

Check these before calling the solution done.

no 0

Missing center

Without echo "0" the halves join with no pivot — keep the center print between both loops.

i = max

Skipped first row

Starting at $i = $max skips the lone 0 row. Outer loop must begin at $max + 1.

PHP_EOL inside

Broken rows

If echo PHP_EOL sits inside either half-loop, the mirror splits across lines. Call it only after the full row.

max = 1

Smallest mirror

Output is 0 then 101 — a good sanity check for bounds and the center print.

max > 9

Multi-digit glue

Values above 9 print multi-digit numbers that run together. Cap demos or add spaces.

fgets

Check is_numeric

Bare (int) casts turn non-numeric strings into 0 — prefer is_numeric before casting.

Analysis

Time and Space Complexity

ProgramTimeExtra space
Fixed / input (Examples 1–2)O(n²)O(1)
Compact max = 3 (Example 3)O(n²)O(1)

There are n + 1 rows for max digit n. Digit total = (n + 1)² → O(n²) time. Only a few loop variables are needed.

Remember

Key Takeaways

  • Three parts: print $i..$max, then 0, then $max..$i.
  • Start at max+1: the first row is only 0; then both halves grow.
  • Break the row: digits and center with no newline; echo PHP_EOL after the full row.
  • Complexity: O(n²) time from (n+1)² digits; O(1) extra space.

One line: for each $i from $max+1 down to 1, print $i..$max, then 0, then $max..$i, then echo PHP_EOL.

Frequently Asked Questions

A 0-centered descending mirror: for max=9 you get 0 / 909 / 89098 / … / 1234567890987654321 — each row mirrors around a fixed zero.
echo "0" sits between the ascending and descending loops, creating a fixed center on every row.
When $i = $max + 1, both side loops are empty — only 0 is printed.
Starting at $max + 1 gives the single-0 row first; then $i decreases and both halves grow toward $max.
Program 27 mirrors 1..$i on each row. Program 28 uses a fixed 0 center and grows digits toward $max on both sides as $i decreases.
Use echo $j . " " and echo $k . " " in the loops instead of echo $j.
Use trim(fgets(STDIN)) and check is_numeric($input) before casting to int, then clamp $max to 1..9 — see Example 2.
O(n²) for max digit n because there are n+1 rows and the digit total is (n+1)².

Did you know?

This pattern prints ascending digits from $i to $max, a fixed 0 in the center, then descending digits from $max down to $i. As $i decreases, each row grows into the long mirror 1234567890987654321.

Next: Spaced Mirror Number Pattern

Continue with a mirror pattern that separates digits with spaces.

Program 29 tutorial →

About the author

Mari Selvan M P
Mari Selvan M P 🔗

Developer, cloud engineer, and technical writer

  • Experience 12 years building web and cloud systems
  • Focus Full Stack Development, AWS, and Developer Education

I write practical tutorials so students and working developers can learn by doing—from databases and APIs to deployment on AWS.

AWS Certified Developer – Associate (Credly)

12 people found this page helpful

PHP Number Pattern 27 — Palindrome Number Triangle PHP Number Pattern 29 — Spaced Mirror Number Pattern