A right-angled triangle star pattern prints a left-aligned staircase of * characters: row i has exactly i stars.
Remember
Rule: on row i, print i stars
*
**
***
****
***** ← 5 rows
In C# you solve it with two nested for loops: the outer loop picks the row, the inner loop prints stars on that row, then Console.WriteLine() moves to the next line. Once this clicks, inverted triangles, pyramids, and hollow shapes become much easier.
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 = rows, inner = stars via Console.Write
Learning, interviews, exams
new string('*', i)
Build a whole row in one call
Shorter demos once loops click
Pseudocode
Pseudocode
for i from 1 to rows:
for j from 1 to i:
print "*" (no newline)
print newline
Change the row count and the triangle updates instantly — including the triangular star total.
Whole numbers from 1 to 20. Tap a chip or type a value — the preview redraws as you go.
Live result5 rows · 15 stars
*
**
***
****
*****
Trace
Worked Walkthrough — rows = 4
Trace each outer-loop value of i and count how many times the inner loop runs.
i
Inner j
Printed row
Stars
1
1..1
*
1
2
1..2
**
2
3
1..3
***
3
4
1..4
****
4
Total star prints: 1 + 2 + 3 + 4 = 10 = 4×5/2. That triangular sum is why time is 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 — ideal for first demos and screenshots.
C#
using System;
class Program
{
static void Main()
{
int rows = 5;
for (int i = 1; i <= rows; i++)
{
for (int j = 1; j <= i; j++)
{
Console.Write("*");
}
Console.WriteLine();
}
}
}
Output
*
**
***
****
*****
How It Works
1. Set height.rows = 5 means the triangle has five lines.
2. Outer loop picks the row.i runs from 1 to rows.
3. Inner loop prints stars. For each i, j runs from 1 to i, so row i gets exactly i stars via Console.Write("*").
4. Break the line.Console.WriteLine() after the inner loop starts the next row.
When i = 1 you get *; when i = 2 you get **; and so on up to 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 <= i; j++)
{
Console.Write("*");
}
Console.WriteLine();
}
}
}
Output (when user enters 7)
Enter the number of rows: 7
*
**
***
****
*****
******
*******
How It Works
1. Prompt and read. Ask for a row count, then convert the line to an int.
2. Same nested-loop 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('*', i)
Build each row in one call — same shape, no explicit inner star loop.
C#
using System;
class Program
{
static void Main()
{
int rows = 5;
for (int i = 1; i <= 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 row.new string('*', i) creates a string of length i filled with stars.
3. Print and advance.WriteLine prints that string 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.
WriteLine inside
Column of stars
If WriteLine is inside the inner loop, each star lands on its own line. Use Write for stars; WriteLine only after the inner loop.
j <= rows
Rectangle, not triangle
Inner bound must be j <= i. j <= rows prints a filled rectangle.
No WriteLine
One endless line
Omitting the row break glues every star onto a single line.
rows = 1
Single star
Output is just * on one line — a good sanity check.
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 loops (Examples 1–2)
O(rows²)
O(1)
new string('*', i) (Example 3)
O(rows²)
O(rows) per temporary row string
Total stars printed = 1 + 2 + … + n = n(n+1)/2, which is still quadratic in n.
Remember
Key Takeaways
Rule: row i prints exactly i stars.
Two loops: outer = rows, inner = stars with Console.Write.
Break the row: call WriteLine only after the inner loop.
Complexity:O(n²) time from the triangular star count; O(1) extra space for nested loops.
One line: for each row i, print i stars with Write, then WriteLine.
Frequently Asked Questions
The outer loop runs i from 1 to rows. For each row i, the inner loop runs j from 1 to i and prints a star. Row 1 prints 1 star, row 2 prints 2 stars, and so on.
You need one loop for which row you are on and another for how many characters belong on that row. Nested for loops express that directly.
Console.Write stays on the same line. Console.WriteLine ends the current line. Stars use Write; the row break uses WriteLine after the inner loop.
Reverse the outer loop so i runs from rows down to 1, for example for (i = rows; i >= 1; i--). The first line then has rows stars. See Program 2.
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)) prints a full 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 i prints exactly i stars. Total stars for n rows is the triangular number n(n+1)/2 — the same count that makes this pattern O(n²).
