C++ Program to Print Number Pattern

You can print a number pattern in C++ using nested for loops; for example, for (int i = 1; i <= n; i++) { for (int j = 1; j <= i; j++) { std::cout << j << ' '; } std::cout << '\n'; } prints numbers from 1 up to the current line number.

Examples

Input3

Output1 1 2 1 2 3

Input5

Output1 1 2 1 2 3 1 2 3 4 1 2 3 4 5

Input1

Output1

How to Think About It

To print a number pattern, think of rows and columns. Each row number tells how many numbers to print. Use one loop to go through each row, and inside it, another loop to print numbers from 1 up to the current row number.

Algorithm

1

Get the number of rows (n) from the user.

2

Start a loop from 1 to n for each row.

3

Inside this loop, start another loop from 1 to the current row number.

4

Print the inner loop number followed by a space.

5

After the inner loop ends, print a newline to move to the next row.

6

Repeat until all rows are printed.

Code

cpp

#include <iostream>

int main() {
    int n;
    std::cin >> n;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= i; j++) {
            std::cout << j << ' ';
        }
        std::cout << '\n';
    }
    return 0;
}

Output

1 
1 2 
1 2 3 

Dry Run

Let's trace input 3 through the code

1

Input read

n = 3

2

First outer loop iteration (i=1)

Inner loop runs j=1; prints '1 '

3

Print newline after first row

Output: '1 \n'

4

Second outer loop iteration (i=2)

Inner loop runs j=1,2; prints '1 2 '

5

Print newline after second row

Output: '1 \n1 2 \n'

6

Third outer loop iteration (i=3)

Inner loop runs j=1,2,3; prints '1 2 3 '

7

Print newline after third row

Output: '1 \n1 2 \n1 2 3 \n'

i (row)	j (column)	Printed Number
1	1	1
2	1	1
2	2	2
3	1	1
3	2	2
3	3	3

Why This Works

Step 1: Outer loop controls rows

The outer for loop runs from 1 to n, each iteration representing one row of the pattern.

Step 2: Inner loop prints numbers

The inner for loop runs from 1 to the current row number, printing numbers in increasing order.

Step 3: Newline after each row

After printing numbers for a row, std::cout << '\n' moves the cursor to the next line for the next row.

Alternative Approaches

Reverse number pattern

cpp

#include <iostream>

int main() {
    int n;
    std::cin >> n;
    for (int i = n; i >= 1; i--) {
        for (int j = 1; j <= i; j++) {
            std::cout << j << ' ';
        }
        std::cout << '\n';
    }
    return 0;
}

Prints numbers starting from n down to 1 rows, showing a decreasing pattern.

Print same number in each row

cpp

#include <iostream>

int main() {
    int n;
    std::cin >> n;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= i; j++) {
            std::cout << i << ' ';
        }
        std::cout << '\n';
    }
    return 0;
}

Prints the row number repeatedly in each row instead of counting up.

Complexity: O(n^2) time, O(1) space

Time Complexity

The nested loops run approximately n*(n+1)/2 times, which is O(n^2), because for each row i, the inner loop runs i times.

Space Complexity

The program uses constant extra space, O(1), as it only stores loop counters and prints output directly.

Which Approach is Fastest?

All approaches use nested loops with similar time complexity; differences are mainly in output style, not performance.

Approach	Time	Space	Best For
Counting up pattern	O(n^2)	O(1)	Simple increasing number patterns
Reverse number pattern	O(n^2)	O(1)	Decreasing rows pattern
Same number per row	O(n^2)	O(1)	Patterns with repeated numbers per row