A descending repeating number triangle prints digit i repeated rows - i + 1 times, counting i down from rows.
Remember
Rule: for i = n..1, print i exactly (n - i + 1) times
5
44
333
2222
11111 ← 5 rows
In C# you solve it with two nested for loops: the outer loop picks the digit, the inner loop repeats it with Console.Write, then WriteLine() ends the row. Program 9 is the ascending twin (1, 22, 333…).
Approach
How to Solve It
Two ways to emit the same shape — start with nested loops, then optionally shorten with new string.
Method
Idea
Best for
Nested loops
Outer picks digit n..1; inner repeats it n-i+1 times
Learning, interviews, exams
new string
Build a whole repeated-digit row in one call
Shorter demos once loops click
Pseudocode
Pseudocode
for i from rows down to 1:
for j from rows down to i:
print i (no newline)
print newline
Cheat sheet
Goal
Pattern
Pick digit (count down)
for (i = rows; i >= 1; i--)
Repeat digit i
for (j = rows; j >= i; j--) Console.Write(i);
End the row
Console.WriteLine();
One-line row shortcut
Console.WriteLine(new string(i.ToString()[0], rows - i + 1));
Ascending twin (Program 9)
for (i = 1; i <= rows; i++) with Write(i) repeated i times
Write vs WriteLine
API
Effect
Use for
Console.Write
Stays on the same line
Each repeat of digit i
Console.WriteLine
Ends the current line
After the inner loop
Try it
Live Preview
Change the row count and the repeating triangle updates instantly — including the total digit count.
Whole numbers from 1 to 9 (single digits). Tap a chip or type a value — the preview redraws as you go.
Live result5 rows · 15 digits
5
44
333
2222
11111
Trace
Worked Walkthrough — rows = 4
Trace each outer-loop value of i, how many times the inner loop runs, and the printed row.
i
Inner j
Repeats
Printed row
4
4..4
1
4
3
4..3
2
33
2
4..2
3
222
1
4..1
4
1111
Total digits are 1+2+3+4 = 10 — the triangular number n(n+1)/2.
Code
C# Programs
Three complete programs: fixed height, row-count input, and a new string shortcut. Use View Output for sample results.
Example 1 — Fixed rows = 5
Outer loop picks the digit; inner loop repeats it rows - i + 1 times.
C#
using System;
namespace MyApp
{
class Program
{
static void Main(string[] args)
{
int rows = 5;
int i, j;
for (i = rows; i >= 1; i--)
{
for (j = rows; j >= i; j--)
{
Console.Write(i);
}
Console.WriteLine();
}
}
}
}
Output
5
44
333
2222
11111
How It Works
1. Count down.for (i = rows; i >= 1; i--) yields 5, 4, 3, 2, 1 — the digit for each row.
2. Grow repeats. When i = 5, the inner loop runs once (5); when i = 1, it runs five times (11111).
3. Newline.WriteLine() after the inner loop starts the next longer row of a smaller digit.
Example 2 — User Input
Read the row count at runtime. Prefer int.TryParse in real apps so bad input does not throw.
C#
using System;
namespace MyApp
{
class Program
{
static void Main(string[] args)
{
int rows;
int i, j;
Console.Write("Enter the number of rows: ");
if (!int.TryParse(Console.ReadLine(), out rows) || rows < 1)
{
Console.WriteLine("Please enter a positive whole number.");
return;
}
for (i = rows; i >= 1; i--)
{
for (j = rows; j >= i; j--)
{
Console.Write(i);
}
Console.WriteLine();
}
}
}
}
2. Same nested loops. Four rows start at 4 and end at 1111.
Example 3 — new string Shortcut
Build each repeated-digit row in one call. Best for single-digit rows (1–9).
C#
using System;
namespace MyApp
{
class Program
{
static void Main(string[] args)
{
int rows = 5;
for (int i = rows; i >= 1; i--)
{
Console.WriteLine(new string(i.ToString()[0], rows - i + 1));
}
}
}
}
Output
5
44
333
2222
11111
How It Works
1. Repeat a char.new string(i.ToString()[0], rows - i + 1) builds a string of the digit character repeated the right count.
2. Same shape. Identical output to Example 1 — keep the two-loop version for exams that ask for both bounds.
Edge Cases & Pitfalls
Check these before calling the solution done.
wrong twin
for (i = 1; i <= rows; i++) with Write(i) × i
That is Program 9 (1, 22, 333). Keep counting down and growing repeats for this pattern.
WriteLine early
WriteLine(i) inside the inner loop
That puts each digit on its own line. Use Write(i); call WriteLine() only after the row finishes.
wrong count
j <= i instead of j >= i
The inner bound must be for (j = rows; j >= i; j--) so repeat count equals rows - i + 1.
rows = 1
Single digit
Output is just 1 — a good sanity check.
rows ≤ 0
Empty output
The outer loop never runs. Validate and prompt again for clearer UX.
multi-digit
rows > 9
Write(10) prints two characters. Labs usually stick to 1–9; the new string shortcut also assumes a single digit char.
Analysis
Time and Space Complexity
Program
Time
Extra space
Nested loops (Examples 1–2)
O(n²)
O(1)
new string shortcut (Example 3)
O(n²)
O(n) per row for the built string
There are n rows printing 1+2+…+n digits, so total work is n(n+1)/2.
Remember
Key Takeaways
Rule: for i = n..1, print digit i exactly n - i + 1 times.
Inner bound:j from rows down to i grows the repeat count as the digit shrinks.
Write vs WriteLine: repeats stay on the line; WriteLine advances after each row.
Next step: Program 11 inverts the triangle (longest row of the top digit first).
One line: for each digit from n down to 1, print it n-i+1 times with Write, then WriteLine.
Frequently Asked Questions
The outer loop decreases i from rows down to 1. The inner loop runs j from rows down to i, so it executes once when i equals rows, twice when i is rows-1, and so on until rows times for i = 1.
for (j = rows; j >= i; j--) runs (rows - i + 1) times. That count grows as i shrinks, which is why 4 prints twice, 3 prints three times, and 1 prints rows times.
Console.Write stays on the same line. Console.WriteLine ends the current line. Repeated digits use Write(i); the row break uses WriteLine after the inner loop.
Program 9 grows upward: row i repeats digit i exactly i times (1, 22, 333). Program 10 starts with one copy of the top digit and increases repeats as the digit decreases (5, 44, 333, 2222, 11111).
O(n²) where n is the number of rows. Total Console.Write calls equal 1+2+…+n = n(n+1)/2.
Yes. Console.WriteLine(new string(i.ToString()[0], rows - i + 1)) prints a full single-digit row in one call. Nested loops are better for learning; the string constructor is a handy shortcut later.
Prefer int.TryParse(Console.ReadLine(), out rows) so bad input does not throw FormatException.
The outer loop never runs, so nothing is printed. Validate and prompt again if you want a clear user message.
🤔
Did you know?
Row digit i repeats rows - i + 1 times. The outer loop counts down from rows, so the first row shows one copy of the top digit and the last row repeats 1 for rows times — still O(n²) total prints.
