Alternating Binary Number Triangle (Starting with 1) in C++

What You’ll Learn

The alternating binary number triangle with an ascending inner loop prints each row starting with 1 and alternating 0/1 as width grows. This tutorial covers the shape rule, loop structure, a live preview, algorithm steps, worked C++ examples, edge cases, and complexity.

📝 Problem & Approach

Given a positive integer rows, print an alternating binary number triangle starting with 1: row i has i digits from j % 2 as j counts up from 1 to i.

// rows = 5 (conceptual shape)
// 1
// 10
// 101
// 1010
// 10101

Inputs & Outputs

Minimal workflow

for i from 1 to rows:
    for j from 1 to i:
        print j % 2 (no newline)
    print newline

Approach comparison

🔮 Live Preview

Choose a row count between 1 and 20 and draw the alternating binary triangle in the browser.

Press "Draw pattern".

Examples Gallery

Three complete C++ programs — fixed rows, a flip variant, and a user-input version. Click View Output to reveal sample console results.

#include <iostream>
using namespace std;

int main() {
    int rows = 5;
    int i, j;

    for (i = 1; i <= rows; ++i) {
        for (j = 1; j <= i; ++j) {
            cout << j % 2;
        }
        cout << "\n";
    }

    return 0;
}

1
10
101
1010
10101

#include <iostream>
using namespace std;

int main() {
    int rows = 5;
    int i, j;

    for (i = 1; i <= rows; ++i) {
        for (j = 1; j <= i; ++j) {
            cout << 1 - (j % 2);
        }
        cout << "\n";
    }

    return 0;
}

0
01
010
0101
01010

#include <iostream>
using namespace std;

int main() {
    int rows;
    int i, j;

    cout << "Enter the number of rows: ";
    cin >> rows;

    for (i = 1; i <= rows; ++i) {
        for (j = 1; j <= i; ++j) {
            cout << j % 2;
        }
        cout << "\n";
    }

    return 0;
}

Enter the number of rows: 4
1
10
101
1010

🔎 Worked Walkthrough — rows = 4

Trace each outer-loop value of i and note the j % 2 values printed as j counts up.

Total digit prints: 1 + 2 + 3 + 4 = 10 = 4×5/2.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

💡 Best Practices