Number Pattern in C++

Four number triangles in C++: 1..j, row index, countdown, Floyd (num++). Same loops, different cout.

IntermediateAdvanced Pattern ProgramsExample 5 of 6

number-pattern.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    // Pattern 1: Increasing numbers
11    cout << "\nPattern 1:" << endl;
12    for (int i = 1; i <= rows; i++) {
13        for (int j = 1; j <= i; j++) {
14            cout << j << " ";
15        }
16        cout << endl;
17    }
18    
19    // Pattern 2: Same number in row
20    cout << "\nPattern 2:" << endl;
21    for (int i = 1; i <= rows; i++) {
22        for (int j = 1; j <= i; j++) {
23            cout << i << " ";
24        }
25        cout << endl;
26    }
27    
28    // Pattern 3: Decreasing numbers
29    cout << "\nPattern 3:" << endl;
30    for (int i = 1; i <= rows; i++) {
31        for (int j = i; j >= 1; j--) {
32            cout << j << " ";
33        }
34        cout << endl;
35    }
36    
37    // Pattern 4: Floyd's Triangle
38    cout << "\nPattern 4 (Floyd's Triangle):" << endl;
39    int num = 1;
40    for (int i = 1; i <= rows; i++) {
41        for (int j = 1; j <= i; j++) {
42            cout << num++ << " ";
43        }
44        cout << endl;
45    }
46    
47    return 0;
48}

Output

Enter number of rows: 5

Pattern 1:
1
1 2
1 2 3
1 2 3 4
1 2 3 4 5

Pattern 2:
1
2 2
3 3 3
4 4 4 4
5 5 5 5 5

Pattern 3:
1
2 1
3 2 1
4 3 2 1
5 4 3 2 1

Pattern 4 (Floyd's Triangle):
1
2 3
4 5 6
7 8 9 10
11 12 13 14 15

What's going on

Four number triangles, same nested-loop skeleton, different thing in cout. Sample rows = 5.

Pattern 1 — cout << j: 1 / 1 2 / 1 2 3 / … That's the beginner Number Pattern page.

Pattern 2 — cout << i: 1 / 2 2 / 3 3 3 / 4 4 4 4 / 5 5 5 5 5. The row index, repeated.

Pattern 3 — j from i down to 1: 1 / 2 1 / 3 2 1 / … Last cell of the row is always 1.

Pattern 4 — Floyd. int num = 1; outside both loops, then cout << num++. Numbers keep going: 1 / 2 3 / 4 5 6 / 7 8 9 10 / 11 12 13 14 15.

Put num = 1 inside the outer loop and Floyd dies — every row starts at 1 again.

The loops are identical: i is the row, j <= i is how many cells. Only the printed value changes. That's the whole trick.

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