A right-aligned right-angled triangle keeps the same star counts as Program 1, but adds leading spaces so the right edge stays flush: row i prints rows - i spaces, then i stars.
Remember
Rule: on row i, print (rows - i) spaces, then i stars
* ← 4 spaces + 1 star
**
***
****
***** ← 0 spaces + 5 stars (5 rows)
In C# you use one outer loop for the row and two inner loops: one for spaces, one for stars, then Console.WriteLine() to move down. Every line is exactly rows characters wide. That space loop is the usual step toward centered pyramids.
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
Two inner loops
Spaces via Write(" "), then stars via Write("*")
Learning, interviews, exams
new string
Build padding and stars as strings
Shorter demos once formulas click
Pseudocode
Pseudocode
for i from 1 to rows:
for j from 1 to (rows - i):
print " " (no newline)
for k from 1 to i:
print "*" (no newline)
print newline
Change the row count and the right-aligned triangle updates instantly — including star total and line width.
Whole numbers from 1 to 20. Tap a chip or type a value — each line is that many characters wide.
Live result5 rows · 15 stars · width 5
*
**
***
****
*****
Trace
Worked Walkthrough — rows = 4
Trace spaces, stars, and total width for each outer-loop value of i.
i
Spaces rows - i
Stars
Width
Printed row
1
3
1
4
*
2
2
2
4
**
3
1
3
4
***
4
0
4
4
****
Every row has width 4. Star total: 1 + 2 + 3 + 4 = 10 = 4×5/2. Character prints are still O(n²).
Code
C# Programs
Three complete programs: fixed rows, console input, and a new string shortcut. Use View Output to reveal sample results.
Example 1 — Fixed rows = 5
Hard-coded height — space loop first, then star loop.
C#
using System;
class Program
{
static void Main()
{
int rows = 5;
for (int i = 1; i <= rows; i++)
{
for (int j = 1; j <= rows - i; j++)
{
Console.Write(" ");
}
for (int k = 1; k <= i; k++)
{
Console.Write("*");
}
Console.WriteLine();
}
}
}
Output
*
**
***
****
*****
How It Works
1. Set height.rows = 5 means five lines, each five characters wide.
2. Outer loop picks the row.i runs from 1 to rows.
3. First inner loop prints spaces.j runs from 1 to rows - i, so row i gets rows - i leading spaces.
4. Second inner loop prints stars.k runs from 1 to i — same star counts as Program 1.
5. Break the line.Console.WriteLine() after both inner loops starts the next row.
When i = 1 you get 4 spaces and *; when i = 5 you get 0 spaces and five stars.
Example 2 — User Input Version
Read the row count at runtime. Prefer int.TryParse in real apps (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());
for (int i = 1; i <= rows; i++)
{
for (int j = 1; j <= rows - i; j++)
{
Console.Write(" ");
}
for (int k = 1; k <= i; k++)
{
Console.Write("*");
}
Console.WriteLine();
}
}
}
Output (when user enters 4)
Enter the number of rows: 4
*
**
***
****
How It Works
1. Prompt and read. Ask for a row count, then convert the line to an int.
2. Same space/star core. Only the source of rows changes — the print logic matches Example 1.
3. Safer input tip.Convert.ToInt32 throws on letters or empty input. Prefer:
Safer input
if (!int.TryParse(Console.ReadLine(), out int rows) || rows < 1)
{
Console.WriteLine("Enter a positive whole number.");
return;
}
Example 3 — new string for Spaces and Stars
Build each row’s padding and star run in one call each — same shape, no explicit character loops.
C#
using System;
class Program
{
static void Main()
{
int rows = 5;
for (int i = 1; i <= rows; i++)
{
Console.Write(new string(' ', rows - i));
Console.WriteLine(new string('*', i));
}
}
}
Output
*
**
***
****
*****
How It Works
1. One outer loop. Still walk i from 1 to rows.
2. Build the padding.new string(' ', rows - i) creates the leading spaces (empty when i == rows).
3. Build and print stars.WriteLine(new string('*', i)) prints i stars and ends the line.
Learn the two-loop version first (Examples 1–2) so you can explain both bounds in an interview; treat this as a polish shortcut afterward.
Edge Cases & Pitfalls
Check these before calling the solution done.
No spaces
Looks like Program 1
Skipping the space loop reprints the left-aligned triangle. Print rows - i spaces before the stars.
Swapped bounds
Broken right edge
Spaces must be rows - i and stars i. Swapping them loses the flush right edge.
j < rows - i
Off-by-one padding
Use j <= rows - i. A strict < drops one needed space on most rows.
Tabs
Use real spaces
Print " ", not tabs — tabs break alignment across fonts and editors.
rows = 1
Single star
0 spaces + 1 star — same as Program 1 for n = 1.
rows ≤ 0
Empty output
Outer loop never runs. Validate and re-prompt for interactive programs.
Bad input
Use TryParse
Convert.ToInt32 throws on letters — prefer int.TryParse.
Analysis
Time and Space Complexity
Program
Time
Extra space
Nested space/star loops (Examples 1–2)
O(rows²)
O(1)
new string (Example 3)
O(rows²)
O(rows) per temporary row string
Each of n rows prints Θ(n) characters (spaces + stars). Star count alone is still n(n+1)/2.
Remember
Key Takeaways
Rule: row i prints rows - i spaces, then i stars.
Two inner loops: padding first, then stars with Console.Write.
Width check: every row has length rows before WriteLine.
Complexity:O(n²) time; O(1) extra space for nested loops.
One line: for each row i, print rows - i spaces, then i stars, then WriteLine.
Frequently Asked Questions
The outer loop runs i from 1 to rows. For each row i, print (rows - i) spaces, then i stars. Row 1 has the most padding and one star; the last row has no spaces and rows stars.
Spaces and stars follow different formulas. One loop prints spaces from 1 to rows minus i; another prints stars from 1 to i. Without the space loop, output stays left-aligned like Program 1.
Console.Write stays on the same line. Console.WriteLine ends the current line. Spaces and stars use Write; the row break uses WriteLine after both inner loops.
Program 1 prints only i stars per row. Program 3 prints (rows - i) spaces first, then i stars, so the same star counts sit flush on the right.
O(n²) where n is the number of rows. Each of n rows prints about n characters (spaces plus stars).
Yes. Console.Write(new string(' ', rows - i)) then Console.WriteLine(new string('*', i)) builds each row without explicit inner character loops.
Prefer int.TryParse(Console.ReadLine(), out rows) so bad input does not throw FormatException.
The right edge no longer stays flush. Keep spaces = rows - i and stars = i.
🤔
Did you know?
Right-aligned and left-aligned triangles use the same star counts per row; only leading spaces change. Each row prints exactly rows characters before the newline: (rows - i) + i = rows.
