Left Half Pyramid in C++

Left-half (right-aligned) pyramid in C++. Print (rows-i) space-pairs, then i stars.

BeginnerPattern ProgramsExample 2 of 6

left-half-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 <= i; j++) {
17            cout << "* ";
18        }
19        cout << endl;
20    }
21    
22    return 0;
23}

Output

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

What's going on

Same star counts as the right-half pyramid, shoved right with spaces. Row i: (rows − i) space-pairs, then i stars.

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

Spaces first:

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

cout << " ";

Two spaces per pad so they line up with "* " (star plus space). One space and the triangle leans.

Then the same star loop as right-half: j from 1 to i, "* ".

Walk 5:

i=1: 4 pads, 1 star

i=2: 3 pads, 2 stars

i=3: 2 pads, 3 stars

i=4: 1 pad, 4 stars

i=5: 0 pads, 5 stars — flush left

Print spaces before stars. Stars first and you get the right-half again.

rows - i going negative never happens here because i ≤ rows.

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