Inverted Pyramid in C++

Inverted star pyramid in C++. Count i down from rows. Same 2*i-1 stars as the full pyramid.

IntermediatePattern ProgramsExample 4 of 6

inverted-pyramid.cpp

1#include <iostream>
2using namespace std;
3
4int main() {
5    int rows;
6    
7    cout << "Enter number of rows: ";
8    cin >> rows;
9    
10    for (int i = rows; i >= 1; i--) {
11        // Print spaces
12        for (int j = 1; j <= rows - i; j++) {
13            cout << " ";
14        }
15        // Print stars
16        for (int j = 1; j <= 2 * i - 1; j++) {
17            cout << "*";
18        }
19        cout << endl;
20    }
21    
22    return 0;
23}

Output

Enter number of rows: 5
*********
 *******
  *****
   ***
    *

What's going on

Full pyramid upside down. Start wide, get narrow. Outer loop counts down.

for (int i = rows; i >= 1; i--)

i = 5, 4, 3, 2, 1 when rows is 5.

Spaces: j <= rows - i. When i is 5 that's 0 spaces. When i is 1 that's 4 spaces. The peak of the inverted triangle is the last line.

Stars: j <= 2 * i - 1, "*". Same odd counts, reverse order: 9, 7, 5, 3, 1.

Walk 5:

i=5: 0 spaces, 9 stars

i=4: 1 space, 7 stars

i=3: 2 spaces, 5 stars

i=2: 3 spaces, 3 stars

i=1: 4 spaces, 1 star

i++ instead of i-- and you reprint the full pyramid. i >= 0 adds a garbage row.

This is the full-pyramid inner loops with a countdown outer loop. Don't rewrite the star formula.

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