Descending Number Triangle in PHP
What You’ll Learn
How to print a descending number triangle in PHP using nested for loops. Each row starts at 1 and prints up to a decreasing limit: $rows, $rows-1, ..., down to 1.
This pattern is a simple way to understand how the outer loop controls rows and the inner loop controls how many numbers appear per row.
⭐ Pattern Output
For $rows = 5, the pattern looks like this:
12345
1234
123
12
1Complete PHP Program
The outer loop starts from $rows and counts down. The inner loop prints numbers from 1 to the current row limit.
<?php
$rows = 5;
for ($i = $rows; $i >= 1; $i--) {
for ($j = 1; $j <= $i; $j++) {
echo $j;
}
echo PHP_EOL;
}🧠 How It Works
Choose the row count
$rows = 5; sets how many lines will be printed.
Outer loop (descending rows)
for ($i = $rows; $i >= 1; $i--) controls the triangle height and ensures each next row has one fewer number than the previous.
Inner loop (print 1..$i)
for ($j = 1; $j <= $i; $j++) prints digits from 1 up to the current row limit $i using echo $j;.
New line
echo PHP_EOL; moves to the next row after each line.
Descending number triangle
Total numbers printed: 1+2+…+n = n(n+1)/2, so time complexity is O(n²) for n rows.
Variation — User Input (CLI) Version
Let the user decide the number of rows at runtime using standard input (run from terminal with php):
<?php
echo "Enter the number of rows: ";
$rows = (int) trim(fgets(STDIN));
for ($i = $rows; $i >= 1; $i--) {
for ($j = 1; $j <= $i; $j++) {
echo $j;
}
echo PHP_EOL;
}💡 Tips for Enhancement
Try These
- Validate input (reject
$rows < 1) before printing the pattern - Print the ascending triangle by counting the outer loop up
- Add spaces between numbers (for example,
echo $j . " ";) - Right-align the triangle by printing leading spaces before each row
- Replace numbers with characters to create alphabet patterns
Avoid
- Forgetting the newline after each row
- Using negative or zero rows without validating input
- Mixing row/column logic (keep the outer loop for rows)
- Assuming CLI input is always valid (guard
fgets()and casting if needed)
Key Takeaways
The outer loop decreases the row length (from $rows down to 1).
The inner loop prints numbers from 1 to the current row limit $i.
Total printed digits follow the triangular number count: n(n+1)/2.
The same nested-loop idea applies to star triangles and alphabet triangles.
❓ Frequently Asked Questions
12345, then 1234, then 123, and so on until 1.$i (from $rows down to 1). The inner loop prints $j from 1 to $i, then echo PHP_EOL; moves to the next line.for ($i = 1; $i <= $rows; $i++) as the outer loop. Each row will then grow from 1 number up to $rows numbers.Explore More PHP Number Patterns!
From pyramids to Floyd’s triangle and beyond—practice nested loops with progressively richer patterns.
The total number of printed digits grows like a triangular number. If you print n rows, the total count is 1+2+…+n = n(n+1)/2. For n = 5, that’s 15 digits.
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