nested-loop-patterns.cpp

/*
 * ============================================================================
 * Topic : Nested loop patterns
 * Level : Basics — nested loops
 * ----------------------------------------------------------------------------
 * What you'll learn
 *   Control spaces and symbols with nested for-loops to draw text art.
 *   See how the outer loop owns the row and the inner loops fill columns.
 *   Practise off-by-one thinking when sliding markers like '$' inward.
 * ----------------------------------------------------------------------------
 * How to run
 *   • OnlineGDB: https://www.onlinegdb.com/online_c++_compiler
 *     Open this file on GitHub → copy → paste into OnlineGDB → C++ → Run
 *   • Codespaces (whole repo): https://codespaces.new/baheesa/cpp-practice?quickstart=1
 *   • Local: g++ -std=c++17 -Wall -o app "01-basics/nested-loop-patterns.cpp" && ./app
 * ----------------------------------------------------------------------------
 * Example input
 *   (no input)
 * Example output
 *   Pattern 1:
 *   #####$
 *   ####$#$#####
 *   ... (symmetric $/# rows)
 *
 *   Pattern 2:
 *   BBBBBBBBB
 *     BBBBBBB
 *       BBBBB
 *         ...
 * ============================================================================
 */

#include <iostream>
using namespace std;

void patternDollarHash() {
    // Each row: left #'s, a $, optional middle #'s + right $, then right #'s.
    // As i grows, left/right # shrink and the middle gap between the two $ grows.
    const int n = 6;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n - 1 - i; j++) cout << '#';  // left wing shrinks
        cout << '$';
        for (int j = 0; j < 2 * i - 1; j++) cout << '#'; // middle (empty on row 0)
        if (i > 0) cout << '$';                            // second $ appears from row 1
        for (int j = 0; j < n - 1 - i; j++) cout << '#';  // right wing mirrors left
        cout << '\n';
    }
}

void patternBTriangle() {
    // Start wide (9 B's), indent by 2 spaces each row, drop 2 B's each row.
    // Two loop variables update together: spaces ↑, bs ↓.
    for (int spaces = 0, bs = 9; bs >= 1; spaces += 2, bs -= 2) {
        for (int s = 0; s < spaces; s++) cout << ' ';
        for (int b = 0; b < bs; b++) cout << 'B';
        cout << '\n';
    }
}

int main() {
    cout << "Pattern 1:\n";
    patternDollarHash();
    cout << "\nPattern 2:\n";
    patternBTriangle();
    return 0;
}