Concentric Number Pattern in C++
What You’ll Learn
How to print a concentric-style number pattern in C++ where the value decreases as you move toward the center, and then increases again.
For k = 5, each row mirrors around the center to form a sequence like:
5 4 3 2 1 2 3 4 5
⭐ Pattern Output
For k = 5, the pattern looks like this:
5 5 5 5 5 5 5 5 5
5 4 4 4 4 4 4 4 5
5 4 3 3 3 3 3 4 5
5 4 3 2 2 2 3 4 5
5 4 3 2 1 2 3 4 5Complete C++ Program
The left half prints from k down to 1, the right half prints from 2 up to k. For each row, the minimum value allowed is the row index i.
#include <iostream>
using namespace std;
int main() {
int i, j;
int k = 5;
for (i = k; i >= 1; i--) {
for (j = k; j >= 1; j--) {
if (j > i)
cout << j << " ";
else
cout << i << " ";
}
for (j = 2; j <= k; j++) {
if (j > i)
cout << j << " ";
else
cout << i << " ";
}
cout << "\n";
}
return 0;
}🧠 How It Works
Set the max value
k = 5 decides the outer value and also the number of rows.
Row loop chooses i
The outer loop runs i from k down to 1. Smaller i means the center gets smaller.
Left half prints k..1 with a floor
We iterate j from k down to 1. If j > i we print j, otherwise we print i.
Right half mirrors 2..k
The second inner loop prints from 2 up to k using the same rule, which mirrors the row around the center.
Concentric look
The minimum value moves toward the center as the rows progress, creating a layered effect.
Variation — User Input Version
Let the user choose k. The width becomes 2*k-1.
#include <iostream>
using namespace std;
int main() {
int k;
cout << "Enter the value of k: ";
cin >> k;
if (k <= 0) return 0;
for (int i = k; i >= 1; i--) {
for (int j = k; j >= 1; j--) {
cout << ((j > i) ? j : i) << " ";
}
for (int j = 2; j <= k; j++) {
cout << ((j > i) ? j : i) << " ";
}
cout << "\n";
}
return 0;
}💡 Tips for Enhancement
Try These
- Remove the trailing spaces by building each row into a string first
- Print as a full square (height
2*k-1) to make a classic concentric square - Replace numbers with letters to create an alphabet version
- Format with
setw()if you print multi-digit numbers - Validate input with
cin.fail()for robustness
Avoid
- Hard-coding 5 everywhere if you want to scale the pattern
- Mixing spaces and tabs (alignment changes across terminals)
- Using
endlinside loops (extra flushing) - Printing negative or zero sizes without handling
Key Takeaways
Each row is a mirror of descending then ascending values.
The condition j > i decides whether to print j or clamp to i.
Width is 2*k-1 for this half-square version.
Runtime is O(k²) for size k.
❓ Frequently Asked Questions
i = 1, the clamp value is 1, so the descending half reaches 1 at the center and then mirrors back upward." " after each number, but alignment becomes harder to read for multi-digit values.2*k-1 rows and compute each cell based on the minimum distance to the border (classic concentric square approach).k × (2*k-1) values.Explore More C++ Number Patterns!
Mirror logic like this is useful for many symmetric patterns and matrix-style problems.
You can view each row as taking the maximum of the row’s minimum value (i) and the column label (j), then mirroring it around the center.
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