Hollow Diamond Star Pattern in C#
What You'll Learn
This pattern is Program 7 (inverted hollow V, upper half) followed by the lower half using the same outer idea as Program 8: after i runs 1…rows, run i from rows - 1 down to 1 with the same j and k inner loops and if (i == j) / if (i == k) tests.
Each printed line has width 2 * rows - 1 (for example 9 characters when rows = 5), including trailing spaces after the right star.
⭐ Pattern Output
When you run the program with rows = 5 (each line is 9 characters):
*
* *
* *
* *
* *
* *
* *
* *
* Complete C# Program
Fixed rows = 5 version:
using System;
namespace MyApp
{
class Program
{
static void Main(string[] args)
{
int i, j, k;
int rows = 5;
/* Upper half: i = 1 .. rows */
for (i = 1; i <= rows; i++)
{
for (j = rows; j >= 1; j--)
{
if (i == j)
Console.Write("*");
else
Console.Write(" ");
}
for (k = 2; k <= rows; k++)
{
if (i == k)
Console.Write("*");
else
Console.Write(" ");
}
Console.WriteLine();
}
/* Lower half: avoid duplicate widest row */
for (i = rows - 1; i >= 1; i--)
{
for (j = rows; j >= 1; j--)
{
if (i == j)
Console.Write("*");
else
Console.Write(" ");
}
for (k = 2; k <= rows; k++)
{
if (i == k)
Console.Write("*");
else
Console.Write(" ");
}
Console.WriteLine();
}
}
}
}🧠 How It Works
Upper half (i = 1 … rows)
for (i = 1; i <= rows; i++) runs the hollow widening V: each iteration prints one full row with the two inner loops below, then Console.WriteLine(). At i == rows you get stars at both outer columns of the waist.
Lower half (i = rows - 1 … 1)
for (i = rows - 1; i >= 1; i--) repeats the same nested j / k bodies so the shape narrows again. Starting at rows - 1 avoids printing the widest row twice.
Console.Write on each cell
for (j = rows; j >= 1; j--): if (i == j) Console.Write("*"); else Console.Write(" ");. Then for (k = 2; k <= rows; k++) with the same if / else. When i == 1, only the j loop draws the top and bottom apex stars.
New line and width
After both inner loops, Console.WriteLine() ends the row. Every line has fixed width rows + (rows - 1) = 2 * rows - 1 (including interior spaces).
Full hollow diamond
Line count: rows + (rows - 1) = 2 * rows - 1. Each line does Θ(rows) writes → O(n²) for n = rows, O(1) extra space. Width 2n - 1 scrolls horizontally in the green preview on narrow screens.
Variation — User Input Version
Read rows with Console.ReadLine():
using System;
namespace MyApp
{
class Program
{
static void Main(string[] args)
{
int rows;
int i, j, k;
Console.Write("Enter the number of rows: ");
rows = Convert.ToInt32(Console.ReadLine());
for (i = 1; i <= rows; i++)
{
for (j = rows; j >= 1; j--)
{
if (i == j)
Console.Write("*");
else
Console.Write(" ");
}
for (k = 2; k <= rows; k++)
{
if (i == k)
Console.Write("*");
else
Console.Write(" ");
}
Console.WriteLine();
}
for (i = rows - 1; i >= 1; i--)
{
for (j = rows; j >= 1; j--)
{
if (i == j)
Console.Write("*");
else
Console.Write(" ");
}
for (k = 2; k <= rows; k++)
{
if (i == k)
Console.Write("*");
else
Console.Write(" ");
}
Console.WriteLine();
}
}
}
}💡 Tips for Enhancement
Try These
- Validate
rows >= 1after parsing - Replace
*with#, digits, or custom symbols - Print only the first outer loop for an inverted hollow V (Program 7)
- For a filled diamond, you need rules for the interior (for example distance from the vertical center), not only
i == jandi == k - Use
int.TryParsefor safer input
Avoid
- Starting the second outer loop at
i == rows—you would duplicate the widest row - Claiming
i != j && i != kalone builds a filled diamond (it does not; it inverts the hollow logic incorrectly) - Dropping trailing spaces so columns no longer align to width
2 * rows - 1
Key Takeaways
Upper half = Program 7; lower half = same inners with i counting down from rows - 1.
Widest row appears once, when i == rows in the first loop.
Each row: left edge via j, right edge via k; same tests on both halves.
Line width is always 2 * rows - 1 characters.
Time complexity O(n²) for n = rows.
❓ Frequently Asked Questions
i from 1 to rows. The second runs i from rows - 1 to 1, mirroring that shape. Both use the same j / k loops and diagonal conditions.i == rows in the first loop. Starting the second loop at rows - 1 prevents printing that line twice.n rows: about 2n - 1 lines, each with two inner passes of length Θ(n).Explore More C# Star Patterns!
Programs 7 and 8 are the two halves of this diamond—practice them separately, then combine.
The hollow diamond is a direct composition: Program 7’s loop plus Program 8’s loop with the duplicate middle row removed by starting the second phase at rows - 1.
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