A filled diamond star pattern is a centered solid diamond: an upper pyramid of odd-length star rows, mirrored below, with the widest row printed only once.
Remember
Rule: spaces = rows - i, stars = 2 * i - 1
Grow i to rows, then shrink from rows - 1
*
***
*****
*******
*********
*******
*****
***
* ← rows = 5 (half-height)
In C# you print each row with two inner loops (spaces, then stars), then Console.WriteLine(). Run that once upward and once downward so the shape closes into a diamond.
Approach
How to Solve It
Reuse one row formula for both halves — start with nested loops, then optionally shorten with new string.
Method
Idea
Best for
Nested loops
Spaces loop + stars loop, twice (up then down)
Learning, interviews, exams
new string
Build spaces and stars as whole strings
Shorter demos once loops click
Pseudocode
Pseudocode
for i from 1 to rows: // upper half
print (rows - i) spaces
print (2 * i - 1) stars
print newline
for i from rows - 1 down to 1: // lower half
print (rows - i) spaces
print (2 * i - 1) stars
print newline
Three complete programs: fixed half-height, console input, and a new string shortcut. Use View Output to reveal sample results.
Example 1 — Fixed rows = 5
Hard-coded half-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 <= rows - i; j++)
{
Console.Write(" ");
}
for (int k = 1; k <= 2 * i - 1; k++)
{
Console.Write("*");
}
Console.WriteLine();
}
for (int i = rows - 1; i >= 1; i--)
{
for (int j = 1; j <= rows - i; j++)
{
Console.Write(" ");
}
for (int k = 1; k <= 2 * i - 1; k++)
{
Console.Write("*");
}
Console.WriteLine();
}
}
}
Output
*
***
*****
*******
*********
*******
*****
***
*
How It Works
1. Set half-height.rows = 5 means the diamond peaks at 5 stars wide on each side of center — 9 total lines.
2. Upper half.i runs from 1 to rows. Print rows - i spaces, then 2 * i - 1 stars, then a newline.
3. Lower half.i runs from rows - 1 down to 1 with the same two inner loops — so the widest row is not repeated.
4. Break the line.Console.WriteLine() after both inner loops starts the next row.
Example 2 — User Input Version
Read the half-height 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 <= 2 * i - 1; k++)
{
Console.Write("*");
}
Console.WriteLine();
}
for (int i = rows - 1; i >= 1; i--)
{
for (int j = 1; j <= rows - i; j++)
{
Console.Write(" ");
}
for (int k = 1; k <= 2 * i - 1; 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 two-phase 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 in two calls — same shape, no explicit space/star inner loops.
C#
using System;
class Program
{
static void PrintRow(int rows, int i)
{
Console.Write(new string(' ', rows - i));
Console.WriteLine(new string('*', 2 * i - 1));
}
static void Main()
{
int rows = 5;
for (int i = 1; i <= rows; i++)
{
PrintRow(rows, i);
}
for (int i = rows - 1; i >= 1; i--)
{
PrintRow(rows, i);
}
}
}
Output
*
***
*****
*******
*********
*******
*****
***
*
How It Works
1. One helper for a row.PrintRow writes rows - i spaces, then a line of 2 * i - 1 stars.
2. Same outer structure. Call it upward for i = 1..rows, then downward from rows - 1.
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.
Lower at rows
Doubled middle
If the lower loop starts at rows, the widest line prints twice. Start at rows - 1.
Even stars
Lost center
Use 2 * i - 1 (odd counts). Even widths break left–right symmetry.
Wrong spaces
Not centered
Spaces must be rows - i. Using i spaces leans the diamond the wrong way.
rows = 1
Single star
Upper prints *; lower never runs — correct tiny diamond.
rows ≤ 0
Empty output
Both outer loops skip. 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 helper (Example 3)
O(rows²)
O(rows) per temporary row string
About 2 * rows - 1 lines; each line does Θ(rows) work for spaces and stars. Total stars = rows² + (rows - 1)².
Remember
Key Takeaways
Row formula:rows - i spaces and 2 * i - 1 stars.
Two phases: grow i to rows, then shrink from rows - 1.
Break the row:Write for spaces/stars; WriteLine after both inner loops.
Complexity:O(n²) time for half-height n; O(1) extra space for nested loops.
One line: spaces = rows - i, stars = 2*i - 1, grow then shrink from rows - 1.
Frequently Asked Questions
The first outer loop runs i from 1 to rows. On each row it prints (rows - i) spaces, then (2 * i - 1) stars. That builds the upper centered pyramid. The second outer loop runs i from (rows - 1) down to 1 with the same two inner loops, mirroring the shape so the diamond closes.
The first part already prints the widest row when i equals rows. Starting the second part at rows - 1 continues with the next narrower rows without repeating the middle line.
The filled diamond prints full runs of stars using 2*i-1 stars per row. The hollow diamond uses diagonal conditions so only the outline has stars. Both use an upper phase and a lower phase starting at rows - 1.
Odd widths keep a single center star on each row and grow by one star on each side per step, which keeps left–right symmetry.
With n equal to rows (half-height), there are 2n - 1 printed lines. Each line does Theta(n) work for spaces and stars combined, so overall time is O(n²).
Exactly 2 * rows - 1 lines. The widest line has 2 * rows - 1 stars.
Yes. Upper half is Program 5; lower half uses the same inner loops with i running like Program 6’s inverted idea, but starting at rows - 1.
Prefer int.TryParse(Console.ReadLine(), out rows) and require rows >= 1 so bad input does not throw FormatException.
🤔
Did you know?
The filled diamond is Program 5’s pyramid plus its mirror: same (rows - i) spaces and (2 * i - 1) stars, with the lower half starting at rows - 1 so the widest row prints only once.
