C++ Program to Print Star Pattern

You can print a star 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 << "*"; } std::cout << std::endl; } prints a right-angled triangle of stars.

Examples

Inputn = 3

Output* ** ***

Inputn = 5

Output* ** *** **** *****

Inputn = 1

Output*

How to Think About It

To print a star pattern, think of rows and columns. For each row from 1 to n, print stars equal to the row number. Use one loop for rows and a nested loop for printing stars in each row.

Algorithm

1

Get the number of rows n from the user

2

For each row i from 1 to n, do:

3

For each column j from 1 to i, print a star

4

After printing stars in a row, move to the next line

5

End

Code

cpp

#include <iostream>

int main() {
    int n;
    std::cout << "Enter number of rows: ";
    std::cin >> n;

    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j <= i; ++j) {
            std::cout << "*";
        }
        std::cout << std::endl;
    }

    return 0;
}

Output

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

Dry Run

Let's trace the program for n = 3 to see how stars are printed.

1

Input

User enters n = 3

2

First row

i = 1, print 1 star: *

3

Second row

i = 2, print 2 stars: **

4

Third row

i = 3, print 3 stars: ***

Row (i)	Stars printed
1	*
2	**
3	***

Why This Works

Step 1: Outer loop controls rows

The outer for loop runs from 1 to n, controlling how many rows to print.

Step 2: Inner loop prints stars

The inner for loop runs from 1 to the current row number, printing that many stars.

Step 3: New line after each row

After printing stars for a row, std::cout << std::endl; moves the cursor to the next line.

Alternative Approaches

Using while loops

cpp

#include <iostream>

int main() {
    int n, i = 1;
    std::cout << "Enter number of rows: ";
    std::cin >> n;

    while (i <= n) {
        int j = 1;
        while (j <= i) {
            std::cout << "*";
            ++j;
        }
        std::cout << std::endl;
        ++i;
    }
    return 0;
}

This uses <code>while</code> loops instead of <code>for</code> loops; it is slightly longer but works the same.

Using recursion

cpp

#include <iostream>

void printStars(int count) {
    if (count == 0) return;
    printStars(count - 1);
    std::cout << "*";
}

void printPattern(int row, int n) {
    if (row > n) return;
    printStars(row);
    std::cout << std::endl;
    printPattern(row + 1, n);
}

int main() {
    int n;
    std::cout << "Enter number of rows: ";
    std::cin >> n;
    printPattern(1, n);
    return 0;
}

This recursive approach is elegant but less intuitive for beginners.

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

Time Complexity

The program uses nested loops: the outer loop runs n times and the inner loop runs up to n times, resulting in O(n^2) time.

Space Complexity

The program uses a fixed amount of extra space for variables, so space complexity is O(1).

Which Approach is Fastest?

The nested for loop approach is straightforward and efficient; recursion adds overhead and is less efficient.

Approach	Time	Space	Best For
Nested for loops	O(n^2)	O(1)	Simple and efficient star patterns
While loops	O(n^2)	O(1)	Alternative loop style, same efficiency
Recursion	O(n^2)	O(n)	Elegant but uses more stack space