A growing reverse number triangle prints each row from the row index down to 1 — 1, then 21, then 321, until $rows..1 on the last line.
Rule: for i = 1..rows
print digits i..1
1
21
321
4321
54321 ← rows = 5Unlike Program 5 (prints 1..$i ascending) and Program 6 (suffix growing leftward), here the outer loop counts up and the inner loop counts down. Program 8 continues with 5, 54, 543.
Outer loop: $i from 1 to $rows. Inner loop: echo $j from $i down to 1. End each row with echo PHP_EOL.
| Method | Idea | Best for |
|---|---|---|
| Fixed rows | Hard-code height; outer up, inner down | Labs and demos |
| CLI input | Same loops; read $rows at runtime | Interactive practice |
| Spaced digits | echo $j . " " between numbers | Easier reading |
for i from 1 to rows:
for j from i down to 1:
print j
print newline| Goal | Pattern |
|---|---|
| Set size | $rows = 5; |
| Outer (row length) | for ($i = 1; $i <= $rows; $i++) |
| Inner (countdown) | for ($j = $i; $j >= 1; $j--) echo $j; |
| End the row | echo PHP_EOL; |
| Digits on row i | $i digits |
| API | Effect | Use for |
|---|---|---|
echo $j | Stays on the same line | Each digit in the row |
echo PHP_EOL | Ends the current line | After the inner loop finishes |
Build the full countdown with echo, then break once.
Change the row count and the growing reverse triangle updates instantly.
Trace $rows = 5, row $i = 3 — the inner loop builds 321.
| Step | Loop | Result |
|---|---|---|
| Outer | $i = 3 | Row length = 3 |
| Inner | $j = 3..1 | 321 |
| Break | echo PHP_EOL | Next row starts |
Earlier rows printed 1 and 21. Later rows prepend a larger start digit (4, then 5).
Three complete programs: fixed $rows = 5, CLI input, and spaced digits. Use View Output for sample results.
$rows = 5Hard-coded height — outer loop counts up; inner prints $i..1.
<?php
$rows = 5;
for ($i = 1; $i <= $rows; $i++) {
for ($j = $i; $j >= 1; $j--) {
echo $j;
}
echo PHP_EOL;
}
?>1. Grow the row. When $i = 1, the inner loop prints only 1.
2. Count down. When $i = 3, $j runs 3, 2, 1 → 321.
3. Row break. echo PHP_EOL after the inner loop starts the next line.
Read $rows from the CLI. Prefer is_numeric (shown below).
<?php
echo "Enter the number of rows: ";
$input = trim(fgets(STDIN));
if (!is_numeric($input) || (int) $input < 1) {
echo "Enter a positive whole number." . PHP_EOL;
exit(1);
}
$rows = (int) $input;
for ($i = 1; $i <= $rows; $i++) {
for ($j = $i; $j >= 1; $j--) {
echo $j;
}
echo PHP_EOL;
}
?>1. Validate input. is_numeric rejects letters; require a positive whole number.
2. Same loops. Ascending outer and $i..1 inner match Example 1 — only the source of $rows changes.
3. Scale. For $rows = 4, the last line is 4321.
Same logic; print a space after each digit for easier reading.
<?php
$rows = 5;
for ($i = 1; $i <= $rows; $i++) {
for ($j = $i; $j >= 1; $j--) {
echo $j . " ";
}
echo PHP_EOL;
}
?>1. Same shape. Outer and inner bounds are unchanged.
2. Spacing. echo $j . " " separates digits without changing the sequence.
3. Still one break. echo PHP_EOL after the inner loop ends the row.
Check these before calling the solution done.
$j = 1..$i like Program 5That prints 1, 12, 123. For this pattern keep $j = $i..1.
That changes the triangle order. Keep for ($i = 1; $i <= $rows; $i++).
echo PHP_EOL inside the inner loopThat prints one digit per line. Call echo PHP_EOL only after the inner loop finishes.
Output is one line: 1.
The outer loop never runs. Validate and prompt again for clearer UX.
$rows > 9echo 10 prints two characters and changes visual width. Labs usually stick to 1–9.
| Program | Time | Extra space |
|---|---|---|
| Fixed / input / spaced (Examples 1–3) | O(n²) | O(1) |
There are n rows, and total digits printed are 1 + 2 + … + n = n(n+1)/2, so work is O(n²).
1..$rows, inner $i..1 — each row is a countdown.echo PHP_EOL advances after the inner loop.5, 54, 543 with a descending outer loop.One line: grow the row length, then print from $i down to 1.
Outer loop grows row index $i; inner loop prints $j from $i down to 1 — 1, 21, 321, … O(n²) for $n rows.
Continue with rows like 5, 54, 543.
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