🚀 Mastering Pattern Problems with For Loops (From Simple to Moderately Complex)

If you’re learning programming, you’ve definitely come across pattern problems in coding practice or interviews.
They look like this:

   *

   * *

   * * *

   * * * *

At first glance, they may feel like just printing stars, but solving them teaches you three powerful things:

1. How nested loops work.

2. How to think in terms of rows and columns.

3. How to break down a bigger problem into smaller sub-problems.

Let’s dive in, starting from simple patterns and working our way up to moderately complex ones.

🔹 1. The Foundation: Single Row and Column

Before doing fancy patterns, let’s start simple.

Example: Print 5 stars in a row

#include <stdio.h>
int main() {
    for(int i = 0; i < 5; i++) {
        printf("* ");
    }
    return 0;
}

👉 Output: * * * * *

🔹 2. Right-Angled Triangle (Basic Nested Loop)

Now let’s use nested loops.

#include <stdio.h>
int main() {
    int n = 5;
    for(int i = 1; i <= n; i++) {
        for(int j = 1; j <= i; j++) {
            printf("* ");
        }
        printf("\n");
    }
    return 0;
}

👉 Output:         

*

* * 

* * * 

* * * * 

* * * * * 

🔹 3. Inverted Triangle

Let’s flip it!

#include <stdio.h>
int main() {
    int n = 5;
    for(int i = n; i >= 1; i--) {
        for(int j = 1; j <= i; j++) {
            printf("* ");
        }
        printf("\n");
    }
    return 0;
}

👉 Output:

* * * * * 

* * * * 

* * * 

* * 

* 

🔹 4. Number Triangle

Patterns aren’t just about stars *. You can print numbers too.

#include <stdio.h>
int main() {
    int n = 5;
    for(int i = 1; i <= n; i++) {
        for(int j = 1; j <= i; j++) {
            printf("%d ", j);
        }
        printf("\n");
    }
    return 0;
}

👉 Output:

1

1 2

1 2 3

1 2 3 4

1 2 3 4 5

🔹 5. Pyramid Shape (Moderately Complex)

Now let’s add spaces to center-align stars.

#include <stdio.h>
int main() {
    int n = 5;
    for(int i = 1; i <= n; i++) {
        // Print spaces
        for(int j = 1; j <= n - i; j++) {
            printf("  ");
        }
        // Print stars
        for(int j = 1; j <= 2*i - 1; j++) {
            printf("* ");
        }
        printf("\n");
    }
    return 0;
}

👉 Output:

        * 

      * * * 

    * * * * * 

  * * * * * * * 

* * * * * * * * * 

🔹 6. Diamond Pattern (Level Up!)

A diamond = pyramid + inverted pyramid.

#include <stdio.h>
int main() {
    int n = 5;
    // Upper pyramid
    for(int i = 1; i <= n; i++) {
        for(int j = 1; j <= n - i; j++) {
            printf(" ");
        }
        for(int j = 1; j <= 2*i - 1; j++) {
            printf("*");
        }
        printf("\n");
    }
    // Lower inverted pyramid
    for(int i = n - 1; i >= 1; i--) {
        for(int j = 1; j <= n - i; j++) {
            printf(" ");
        }
        for(int j = 1; j <= 2*i - 1; j++) {
            printf("*");
        }
        printf("\n");
    }
    return 0;
}

👉 Output:

    *

   ***

  *****

 *******

*********

 *******

  *****

   ***

    *

🔹 7. Hollow Square (Moderately Complex)

Adding conditions inside the loop.

#include <stdio.h>
int main() {
    int n = 5;
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < n; j++) {
            if(i == 0 || i == n-1 || j == 0 || j == n-1) {
                printf("* ");
            } else {
                printf("  ");
            }
        }
        printf("\n");
    }
    return 0;
}

👉 Output:

* * * * *

*          *

*          *

*          *

* * * * *

🎯 Key Takeaways

• Outer loop → rows. Inner loop → columns.

• Pattern problems are about thinking in 2D (row × column).

• Adding conditions (like spaces, numbers, or boundaries) makes patterns more interesting.

• Once you master these, you’ll breeze through coding challenges and campus interview questions.

⚡ Challenge for You!

Try to code this pattern by yourself (hint: combine numbers + spaces):

                         1

                       1 2

                      1 2 3

                    1 2 3 4

                  1 2 3 4 5

👉 Once you solve this, you’ve officially mastered moderately complex patterns with for loops in C 🎉