An increasing-start alphabet triangle keeps a fixed end letter on the right and moves the start letter one step later each row — so the left edge slides inward.
Remember
Rule: for start letter i from A to last,
print i through last
ABCDE
BCDE
CDE
DE
E ← 5 rows (right edge fixed at E)
Same widths as Program 5 (5, 4, 3, 2, 1), but Program 5 shortens the end while restarting at A. Here the start advances and the end stays put. Compare also with Program 3, which grows into the same right edge.
Approach
How to Solve It
Two ways to emit the same shape — start with nested char loops, then optionally shorten with Substring.
Method
Idea
Best for
Nested char loops
Outer = advancing start; inner = start..end
Learning, interviews, exams
top.Substring(i)
Drop one left letter each row from a fixed prefix
Shorter demos once loops click
Pseudocode
Pseudocode
end = lastLetter
for start from 'A' to end:
for ch from start to end:
print ch (no newline)
print newline
Cheat sheet
Goal
Pattern
Advance start letter
for (char i = 'A'; i <= end; i++)
Print i..end
for (char j = i; j <= end; j++) Console.Write(j);
End the row
Console.WriteLine();
End letter from rows
char end = (char)('A' + rows - 1);
One-line row shortcut
Console.WriteLine(top.Substring(i)); while i advances
Change the row count and the increasing-start triangle updates instantly — capped at 26 letters (A–Z).
Whole numbers from 1 to 26. Tap a chip or type a value — the preview redraws as you go.
Live result5 rows · 15 letters
ABCDE
BCDE
CDE
DE
E
Trace
Worked Walkthrough — rows = 4
Trace each outer-loop start letter as i advances from 'A' to 'D' with end fixed at 'D'.
Start i
Inner j
Printed row
Letters
'A'
A..D
ABCD
4
'B'
B..D
BCD
3
'C'
C..D
CD
2
'D'
D..D
D
1
Total letter prints: 4 + 3 + 2 + 1 = 10 = 4×5/2 — same triangular count as Programs 1 and 5.
Code
C# Programs
Three complete programs: fixed end letter, console input, and a Substring shortcut. Use View Output to reveal sample results.
Example 1 — Fixed end at 'E'
Hard-coded end letter — outer loop advances the start; inner loop prints i..E.
C#
using System;
class Program
{
static void Main()
{
for (char i = 'A'; i <= 'E'; i++)
{
for (char j = i; j <= 'E'; j++)
{
Console.Write(j);
}
Console.WriteLine();
}
}
}
Output
ABCDE
BCDE
CDE
DE
E
How It Works
1. Outer loop picks the start letter.i runs from 'A' to 'E' — longest row first.
2. Inner loop starts at i. For each start, j runs from i to 'E', so the row is i..E.
3. Print letters, then break the line.Console.Write(j) stays on the row; WriteLine() after the inner loop starts the next (shorter) row.
When i = 'A' you get ABCDE; when i = 'E' you get E.
Example 2 — User Input Version
Read the row count at runtime. Prefer int.TryParse and clamp to 26 (shown in the tip below).
C#
using System;
class Program
{
static void Main()
{
Console.Write("Enter the number of rows: ");
int rows = Convert.ToInt32(Console.ReadLine());
char end = (char)('A' + rows - 1);
for (char i = 'A'; i <= end; i++)
{
for (char j = i; j <= end; j++)
{
Console.Write(j);
}
Console.WriteLine();
}
}
}
Output (when user enters 4)
Enter the number of rows: 4
ABCD
BCD
CD
D
How It Works
1. Prompt and read. Ask for a row count, then convert the line to an int.
2. Map rows to an end letter.end = (char)('A' + rows - 1) — for rows = 4, end is 'D'.
3. Same advance core. Only the source of end changes — the print logic matches Example 1.
4. Safer input tip.Convert.ToInt32 throws on letters. Prefer:
Safer input
if (!int.TryParse(Console.ReadLine(), out int rows) || rows < 1 || rows > 26)
{
Console.WriteLine("Enter a whole number from 1 to 26.");
return;
}
Example 3 — Substring(i)
Drop one left letter each row from a fixed prefix — same shape, no explicit inner letter loop.
C#
using System;
class Program
{
static void Main()
{
int rows = 5;
string letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
string top = letters.Substring(0, rows);
for (int i = 0; i < rows; i++)
{
Console.WriteLine(top.Substring(i));
}
}
}
Output
ABCDE
BCDE
CDE
DE
E
How It Works
1. Build the first row.top = letters.Substring(0, rows) is ABCDE when rows = 5.
2. Slice from index i.top.Substring(0) is the full row; Substring(1) drops A; and so on.
3. Learn loops first. Use Examples 1–2 when you need to show nested bounds; treat this as a polish shortcut afterward.
Edge Cases & Pitfalls
Check these before calling the solution done.
j = 'A'
Program 5 by mistake
If the inner loop starts at 'A' instead of i, you print ABCDE, ABCD, … Use for (char j = i; …).
WriteLine inside
Column of letters
If WriteLine is inside the inner loop, each letter lands on its own line. Use Write for letters; WriteLine only after the inner loop.
Wrong end
Off-by-one end letter
Use (char)('A' + rows - 1). Forgetting - 1 pushes the end past the intended letter.
rows > 26
Past Z
'A' + rows - 1 leaves A–Z when rows > 26. Clamp or reject in interactive programs.
rows = 1
Single A
Output is just A — start and end coincide. A good sanity check.
Bad input
Use TryParse
Convert.ToInt32 throws on letters — prefer int.TryParse and require 1–26.
Analysis
Time and Space Complexity
Program
Time
Extra space
Nested loops (Examples 1–2)
O(rows²)
O(1)
Substring (Example 3)
O(rows²)
O(rows) for the prefix and temporary row strings
Total letters = n + (n - 1) + … + 1 = n(n + 1)/2 — quadratic in n. Same totals as Programs 1 and 5.
Remember
Key Takeaways
Rule: advance start letter i; print i through a fixed end each row.
vs Program 5: same widths — here the left edge moves; there the right edge moves.
Break the row: call WriteLine only after the inner loop.
Complexity:O(n²) time from the triangular letter count; O(1) extra space for nested loops.
One line: for i from 'A' to the end letter, print i through that end, then WriteLine.
Frequently Asked Questions
The outer loop picks the starting letter (A, then B, then C…). The inner loop prints from that start up to a fixed end letter. Each row drops the leftmost character and becomes shorter.
Because the inner loop always stops at the same end letter ('E'), so the last printed character is fixed on the right.
Program 5 restarts each row at A and shortens the end letter (ABCDE, ABCD, …). Program 6 shifts the start letter forward each row while keeping the same end letter (ABCDE, BCDE, …).
Program 3 grows while starting earlier (E, DE, CDE). This pattern shrinks while starting later (ABCDE, BCDE, CDE). Both keep a fixed right edge at the top letter.
Console.Write stays on the same line. Console.WriteLine ends the current line. Letters use Write; the row break uses WriteLine after the inner loop.
O(n²) for n rows, because total printed characters are n(n+1)/2.
Yes. Take letters.Substring(0, rows), then print top.Substring(i) while i runs from 0 to rows-1. Nested char loops are better for learning; Substring is a handy shortcut later.
Prefer int.TryParse(Console.ReadLine(), out rows) and clamp rows between 1 and 26 so bad input does not throw FormatException or walk past Z.
🤔
Did you know?
Each row starts one letter later but always ends at the same letter. For 5 rows: ABCDE, BCDE, CDE, DE, E. Same widths as Program 5, but the left edge moves instead of the right.
