Print letters without a newline, then end the row once.
Try it
Live Preview
Change the row count and the repeating triangle updates instantly — including the triangular letter total.
Whole numbers from 1 to 10. Tap a chip or type a value — the preview redraws as you go.
Live result5 rows · last E · 15 letters
A
BB
CCC
DDDD
EEEEE
Trace
Worked Walkthrough — rows = 4
Trace each row as row advances from 1 to 4.
row
Letter
Printed row
Repeats
1
A
A
1
2
B
BB
2
3
C
CCC
3
4
D
DDDD
4
Total letter prints: 1 + 2 + 3 + 4 = 10 = 4×5/2 — same triangular count as Program 1.
Code
Python Programs
Three complete programs: fixed 5 rows, input() row-count, and a ch * row shortcut. Use View Output to reveal sample results.
Example 1 — Fixed A–E
Hard-coded height — outer loop picks the letter; inner loop only controls the repeat count.
Python
rows = 5
for row in range(1, rows + 1):
ch = chr(ord("A") + row - 1)
for _ in range(row):
print(ch, end="")
print()
Output
A
BB
CCC
DDDD
EEEEE
How It Works
1. Outer loop picks the row.row runs from 1 to 5 — one letter per row.
2. Map row to a letter.ch = chr(ord("A") + row - 1) — for row = 3, ch is C.
3. Inner loop only counts. Print ch exactly row times with end="".
When row = 3 the inner loop runs three times and you get CCC.
Example 2 — Row Count Input
Read the height at runtime. Prefer try/except ValueError and a 1–26 clamp in real apps.
Python
rows = int(input("Enter the number of rows: "))
if rows < 1:
raise SystemExit
if rows > 26:
rows = 26
for row in range(1, rows + 1):
ch = chr(ord("A") + row - 1)
for _ in range(row):
print(ch, end="")
print()
Output (when user enters 4)
Enter the number of rows: 4
A
BB
CCC
DDDD
How It Works
1. Prompt and read. Ask for a row count, then convert with int().
2. Same map and repeat. Letter and width still follow row — only the height comes from input.
3. Safer input tip. Prefer:
Safer input
try:
rows = int(input("Enter the number of rows: "))
except ValueError:
print("Enter a whole number from 1 to 26.")
raise SystemExit
if rows < 1 or rows > 26:
print("Enter a whole number from 1 to 26.")
raise SystemExit
Example 3 — print(ch * row)
Build each repeated-letter row in one expression — same shape, no explicit inner letter loop.
Python
rows = 5
for row in range(1, rows + 1):
ch = chr(ord("A") + row - 1)
print(ch * row)
Output
A
BB
CCC
DDDD
EEEEE
How It Works
1. One outer loop. Still walk row from 1 to rows and map it to a letter.
2. Build the row.ch * row creates a string of length row filled with ch.
3. Print and advance. Bare print(...) prints that string and ends the line.
Learn the two-loop version first (Examples 1–2) so you can explain both bounds; treat this as a polish shortcut afterward.
Edge Cases & Pitfalls
Check these before calling the solution done.
Wrong letter
Program 1 by mistake
If you print stepping letters across the row instead of a fixed ch, you get A, AB, ABC…. Always print the same letter row times.
print() early
Column of letters
If bare print() is inside the inner loop, each letter lands on its own line. Use end="" for letters; call print() only after the inner loop.
Wrong width
Rectangle, not triangle
Inner bound must grow with the row (range(row)). A fixed inner bound prints a filled rectangle.
rows = 1
Single A
Output is just A on one line — a good sanity check.
rows > 26
Beyond Z
Cap or reject — the row letter leaves the alphabet. Keep rows in 1…26 for A–Z demos.
Bad input
Use try/except
int(input()) raises on letters — prefer try/except ValueError and clamp to 1…26.
Analysis
Time and Space Complexity
Program
Time
Extra space
Nested loops (Examples 1–2)
O(n²)
O(1)
ch * row (Example 3)
O(n²)
O(n) per temporary row string
Total letters printed = 1 + 2 + … + n = n(n+1)/2, which is still quadratic in n.
Remember
Key Takeaways
Rule: one letter per row; width grows 1, 2, 3, …
Print one letter: the inner loop only counts — print ch, not stepping letters.
Break the row: call print() only after the inner loop.
Complexity:O(n²) time; O(1) extra space for nested loops.
One line: for each row, print letter A + row - 1 exactly row times, then print().
Frequently Asked Questions
Because the inner loop prints the outer-loop letter (ch) every time. The inner counter only controls how many times to print, not which character to print.
Then letters would change across the row (A, AB, ABC…), which is Program 1 — not a repeating-letter triangle.
On the third row the letter is C (chr(ord('A') + 2)), and the inner loop runs three times, printing C each time.
Program 1 prints stepping letters across each row (A, AB, ABC). This pattern keeps one letter per row and only grows the repeat count (A, BB, CCC).
Program 10 uses the same growing widths but letters count downward (E, DD, CCC…). This pattern counts upward (A, BB, CCC…).
print(ch, end="") stays on the same line. Bare print() ends the current line. Letters use end=""; the row break uses print() after the inner loop.
O(n²) for n rows, because total printed characters are n(n+1)/2.
Yes. print(ch * row) prints a full repeated-letter row in one call. Nested loops are better for learning; ch * row is a handy shortcut later.
🤔
Did you know?
Each row prints the same letter repeatedly: row 1 prints A once, row 2 prints B twice, row 3 prints C three times. Letter = chr(ord('A') + row - 1). The reverse twin is Program 10.
