The powers of 11 pattern prints one number per line, starting at 1 and multiplying by 11 each row.
Rule: res starts at 1; each next row is res * 11
1
11
121
1331
14641 ← n = 5In PHP one loop is enough: keep a running $res, print it, then $res *= 11. No nested loops required.
One loop, one running variable — print, then multiply by 11.
| Method | Idea | Best for |
|---|---|---|
| Print then multiply | echo $res . PHP_EOL; $res *= 11; | Cleanest loop body |
| If on first row | if ($i == 1) $res = 1; else $res *= 11; | Matching older textbook code |
res = 1
for i from 1 to n:
print res
res = res * 11| Goal | Pattern |
|---|---|
| Start value | $res = 1; |
| Loop rows | for ($i = 1; $i <= $n; $i++) |
| Print line | echo $res . PHP_EOL; |
| Next term | $res *= 11; |
| API | Effect | Use for |
|---|---|---|
echo $res . PHP_EOL | Prints the value and ends the line | Preferred — one call per row |
echo $res + echo PHP_EOL | Same result in two calls | Older textbook style (Example 1) |
Same idea as C# WriteLine(res): one value per line. Prefer a single echo $res . PHP_EOL over split print + newline.
Change the row count and the powers-of-11 sequence updates instantly.
$n = 5Trace $res before and after each multiply.
| Row | Then $res *= 11 | |
|---|---|---|
1 | 1 | 11 |
2 | 11 | 121 |
3 | 121 | 1331 |
4 | 1331 | 14641 |
5 | 14641 | 161051 (not printed) |
Total prints = $n. Values grow fast — keep $n small while learning.
Three complete programs: fixed 5 rows with an if-check, user-input rows, and a clean print-then-multiply loop. Use View Output for sample results.
$n = 5Textbook style with a special case on the first row.
<?php
$res = 1;
for ($i = 1; $i <= 5; $i++) {
if ($i == 1)
$res = $i;
else
$res = $res * 11;
echo $res;
echo PHP_EOL;
}1. First row. When $i == 1, set $res = 1 and print it.
2. Later rows. Multiply the previous $res by 11, then print.
3. New line. echo $res + echo PHP_EOL ends each row (or use echo $res . PHP_EOL).
Read $n safely and print the first $n terms.
<?php
echo "Enter number of rows: ";
$input = trim(fgets(STDIN));
if (!is_numeric($input) || (int) $input < 1) {
echo "Please enter a positive whole number." . PHP_EOL;
exit(1);
}
$n = (int) $input;
$res = 1;
for ($i = 1; $i <= $n; $i++) {
if ($i == 1)
$res = 1;
else
$res = $res * 11;
echo $res . PHP_EOL;
}1. Validate n. Check is_numeric; require $n >= 1.
2. Same sequence. Only the loop bound changes from the literal 5.
No special-case if — print first, then update.
<?php
$res = 1;
for ($i = 1; $i <= 5; $i++) {
echo $res . PHP_EOL;
$res *= 11;
}1. Print current. Start with $res = 1; each iteration prints the current value.
2. Advance. $res *= 11 prepares the next row — no if needed.
Check these before calling the solution done.
If you do $res *= 11 before printing when $res starts at 1, the first line becomes 11. Print first.
11^n balloon quickly. Start with small $n (like 5) while learning.
You get 1, 10, 100, 1000… Keep the factor 11.
Output is just 1 — valid and useful for testing.
After 14641, carries appear (161051). Digits no longer match binomial coefficients.
Prefer is_numeric after trim(fgets(STDIN)) so non-numeric input does not silently become 0.
| Program | Time | Extra space |
|---|---|---|
| Fixed / clean (Examples 1, 3) | O($n) | O(1) |
| User input (Example 2) | O($n) | O(1) |
One multiply and one print per row — linear in the number of rows (unlike nested-loop patterns).
echo $res . PHP_EOL; $res *= 11; — no if needed.echo $res . PHP_EOL.$i*$j).One line: print the current power-of-11 term, then multiply by 11 for the next row.
Start with $res = 1, print it, then update with $res *= 11 each row. The first five lines are 1, 11, 121, 1331, 14641 — one value per line, O(n) time.
Print row products $i*1, $i*2, … up to $i*$i.
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