PHP Star Cross Pattern (Over Zeros)

Beginner
5 min read
Updated: Sep 2026
3 programs
Live preview
X pattern with stars on diagonals and center column, zeros elsewhere in PHP
Definition

What Is This Pattern?

An X pattern of stars and zeros fills a rectangular grid: print * on both diagonals and the center column; print 0 everywhere else.

Remember
Rule: * if i==j or j==mid or i==cols+1-j; else 0

*000*000*
0*00*00*0
00*0*0*00
000***000   ← rows = 4, cols = 9

In PHP walk every cell with nested loops. Use $mid = intdiv($cols + 1, 2) and a three-part condition to choose * or 0.

Approach

How to Solve It

One nested loop over the grid, plus a three-way star condition.

MethodIdeaBest for
Diagonals + mid$i==$j / $j==$mid / anti-diagonalLearning, interviews, exams
Sized gridSame logic with $rows, $cols, $midPractice / demos

Pseudocode

Pseudocode
mid = (cols + 1) / 2
for i from 1 to rows:
    for j from 1 to cols:
        if i == j or j == mid or i == cols + 1 - j:
            print "*"
        else:
            print "0"
    print newline

Cheat sheet

GoalPattern
Walk rows / colsfor ($i = 1; $i <= $rows; $i++) / for ($j = 1; $j <= $cols; $j++)
Center column$mid = intdiv($cols + 1, 2)
Star testif ($i == $j || $j == $mid || $i == $cols + 1 - $j)
Print star / fillecho "*" / echo "0"
End the rowecho PHP_EOL

Printing Numbers vs Starting a New Line

APIEffectUse for
echo "*" / echo "0"Stays on the same lineEach cell
echo PHP_EOLEnds the current lineAfter the column loop finishes a row

Print each cell without a newline, then end the row once.

Try it

Live Preview

Change the row count (width becomes 2 × rows + 1) and the X updates instantly.

Whole numbers from 3 to 6. Columns = 2 × rows + 1 (odd width so the center column exists). Tap a chip or type a value — the preview redraws as you go.

Live result 4 × 9 · 36 cells
*000*000*
0*00*00*0
00*0*0*00
000***000
Trace

Worked Walkthrough — $rows = 4, $cols = 9

$mid = 5. Trace why key cells print *.

CellWhy *?Row so far
(1,1)$i == $j (main diagonal)*
(1,5)$j == $mid*000*
(1,9)$i == 10 - $j*000*000*
(4,4)..(4,6)diagonal + mid meet000***000

Every cell is decided once — total prints = $rows × $cols.

Code

PHP Programs

Three complete programs: fixed 4×9, user-input size, and diagonals-only contrast. Use View Output for sample results.

Example 1 — Fixed $rows = 4, $cols = 9

Hard-coded bounds with literals 5 and 10 - $j.

PHP
<?php
for ($i = 1; $i <= 4; $i++) {
    for ($j = 1; $j <= 9; $j++) {
        if ($i == $j || $j == 5 || $i == 10 - $j)
            echo "*";
        else
            echo "0";
    }
    echo PHP_EOL;
}

How It Works

1. Grid walk. Outer $i picks the row; inner $j picks the column.

2. Star test. $i == $j (main), $j == 5 (center), or $i == 10 - $j (anti-diagonal).

3. Fill. Everything else prints 0; echo PHP_EOL ends each row.

Example 2 — User Input (rows & cols)

Read size, compute $mid, and use $cols + 1 - $j for the anti-diagonal.

PHP
<?php
echo "Enter rows: ";
$rowsInput = trim(fgets(STDIN));
if (!is_numeric($rowsInput) || (int) $rowsInput < 1) {
    echo "Please enter a positive whole number." . PHP_EOL;
    exit(1);
}

echo "Enter cols (odd): ";
$colsInput = trim(fgets(STDIN));
if (!is_numeric($colsInput) || (int) $colsInput < 1 || (int) $colsInput % 2 == 0) {
    echo "Please enter a positive odd column count." . PHP_EOL;
    exit(1);
}

$rows = (int) $rowsInput;
$cols = (int) $colsInput;
$mid = intdiv($cols + 1, 2);

for ($i = 1; $i <= $rows; $i++) {
    for ($j = 1; $j <= $cols; $j++) {
        if ($i == $j || $j == $mid || $i == $cols + 1 - $j)
            echo "*";
        else
            echo "0";
    }
    echo PHP_EOL;
}

How It Works

1. Validate size. Require positive rows and an odd $cols so a true center column exists.

2. Same star rule. $mid and $cols + 1 - $j replace the hard-coded 5 and 10 - $j.

Example 3 — Diagonals Only

Drop the center-column check — a pure X without the vertical line.

PHP
<?php
for ($i = 1; $i <= 4; $i++) {
    for ($j = 1; $j <= 9; $j++) {
        if ($i == $j || $i == 10 - $j)
            echo "*";
        else
            echo "0";
    }
    echo PHP_EOL;
}

How It Works

1. Two tests only. Main diagonal $i == $j and anti-diagonal $i == 10 - $j.

2. Compare. The middle column of zeros shows what $j == $mid added in Example 1.

Edge Cases & Pitfalls

Check these before calling the solution done.

even cols

Even column count

There is no single center column. Prefer odd $cols so $mid is exact.

0-based

Loops from 0 with 1-based formulas

If indices are 0-based, adjust to $i == $j, $j == $mid, and $i + $j == $cols - 1.

AND

Use && instead of ||

Almost no cells match all three tests at once. Border stars need ||.

PHP_EOL

echo PHP_EOL inside the column loop

That puts every cell on its own line. Call echo PHP_EOL only after the inner loop.

rows > cols

More rows than columns

The main diagonal exits the grid early. Keep $rows <= $cols for a clear X.

Bad input

Casting without checks

Prefer is_numeric after trim(fgets(STDIN)) so non-numeric input does not silently become 0.

Analysis

Time and Space Complexity

ProgramTimeExtra space
Fixed / diagonals (Examples 1, 3)O($rows × $cols)O(1)
User input (Example 2)O($rows × $cols)O(1)

Every cell of the grid is visited once, so work is proportional to the product of rows and columns.

Remember

Key Takeaways

  • Rule: * on main diagonal, anti-diagonal, and center column; 0 elsewhere.
  • Size: prefer odd $cols; $mid = intdiv($cols + 1, 2); anti-diagonal uses $cols + 1 - $j.
  • echo vs PHP_EOL: each cell stays on the line; echo PHP_EOL advances after each row.
  • Next step: Program 46 prints a concentric number square (5..1..5).

One line: visit every cell; print * on the X and center, 0 everywhere else.

Frequently Asked Questions

An X-style grid: * on both diagonals and the center column, with 0 filling the remaining cells (classic demo: 4×9).
With $cols = 9, $mid = intdiv($cols + 1, 2) = 5. Checking $j == $mid draws the vertical center line.
Main diagonal: $i == $j. Anti-diagonal: $i == $cols + 1 - $j (for $cols = 9 that is $i == 10 - $j).
Program 44 prints a centered number diamond. Program 45 prints a rectangular * / 0 grid using diagonal and center conditions.
Use $rows and $cols variables, compute $mid = intdiv($cols + 1, 2), and use $cols + 1 - $j for the anti-diagonal — see Example 2.
O($rows × $cols) because each cell is visited once.
Yes — drop the $j == $mid check for a pure X of diagonals only — see Example 3.
For 1-based indexing, row $i meets column $j on the anti-diagonal when $i + $j equals $cols + 1.
Use trim(fgets(STDIN)) and check is_numeric($input) before casting to int — see Example 2.

Did you know?

Print * when $i == $j, $j == $mid, or $i == $cols + 1 - $j; otherwise print 0. A $rows × $cols grid visits every cell once.

Next: Concentric Number Square

Print values that decrease toward the center and mirror back out (5..1..5).

Program 46 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)

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PHP Number Pattern 44 — Number Diamond Pattern PHP Number Pattern 46 — Concentric Number Square