Full Pyramid in C++

Centered star pyramid in C++. Row i: rows-i spaces, then 2*i-1 stars.

IntermediatePattern ProgramsExample 3 of 6

full-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 = 1; i <= rows; 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

A centered triangle: odd star counts 1, 3, 5, 7, 9. Row i has rows - i single spaces, then 2 * i - 1 stars with no extra space between them.

for (int i = 1; i <= rows; i++)

for (int j = 1; j <= rows - i; j++) cout << " ";

One space. Not " ". The stars are "*" not "* ", so the pad is half as wide.

for (int j = 1; j <= 2 * i - 1; j++) cout << "*";

Walk 5:

i=1: 4 spaces, 1 star

i=2: 3 spaces, 3 stars

i=3: 2 spaces, 5 stars

i=4: 1 space, 7 stars

i=5: 0 spaces, 9 stars

2 * i - 1 is 1, 3, 5, 7, 9. Use i here and you reprint the right-half, just centered a bit.

Inverted pyramid is this loop running i from rows down to 1.

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