🟢 Beginner · Lesson 16

Pattern Programs

Understanding Pattern Programs

Pattern programs are a classic way to practice nested loops. The key insight is:

Outer loop → controls the number of rows
Inner loop → controls the number of columns (characters per row)
The relationship between the row number and column count determines the shape

💡 Strategy to Solve Any Pattern

Look at the pattern — how many rows?
In each row, what's printed and how many times?
Find the relationship between row number (i) and column count (j)
Write outer loop for rows, inner loop(s) for columns

Star Patterns

Pattern 1: Right Triangle (Increasing)

C Language

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

* * * * * * * * * * * * * * *

Pattern 2: Inverted Right Triangle

C Language

int n = 5;
for (int i = n; i >= 1; i--) {     // i starts from n, counts down
    for (int j = 1; j <= i; j++)
        printf("* ");
    printf("\n");
}

* * * * * * * * * * * * * * *

Pattern 3: Square Pattern

C Language

int n = 4;
for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= n; j++)   // Always n columns
        printf("* ");
    printf("\n");
}

* * * * * * * * * * * * * * * *

Pattern 4: Hollow Rectangle

C Language

int rows = 4, cols = 6;
for (int i = 1; i <= rows; i++) {
    for (int j = 1; j <= cols; j++) {
        if (i == 1 || i == rows || j == 1 || j == cols)
            printf("* ");   // Border only
        else
            printf("  ");   // Interior spaces
    }
    printf("\n");
}

* * * * * * * * * * * * * * * *

Number Patterns

Pattern 5: Floyd's Triangle

C Language

int n = 5, num = 1;
for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= i; j++)
        printf("%3d", num++);   // num increases continuously
    printf("\n");
}

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Pattern 6: Number Triangle (1 to i)

C Language

for (int i = 1; i <= 5; i++) {
    for (int j = 1; j <= i; j++)
        printf("%d ", j);
    printf("\n");
}

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

Pattern 7: Same Number Each Row

C Language

for (int i = 1; i <= 5; i++) {
    for (int j = 1; j <= i; j++)
        printf("%d ", i);   // Print row number i times
    printf("\n");
}

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

Alphabet Patterns

Pattern 8: Alphabet Triangle

C Language

for (int i = 1; i <= 5; i++) {
    for (int j = 0; j < i; j++)
        printf("%c ", (char)('A' + j));  // A B C D E
    printf("\n");
}

A A B A B C A B C D A B C D E

Pyramid Patterns (Centered)

Pattern 9: Centered Star Pyramid

C Language

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

* *** ***** ******* *********

Pattern 10: Diamond Pattern

C Language

#include <stdio.h>
int main() {
    int n = 4;
    // Upper half
    for (int i = 1; i <= n; i++) {
        for (int s = 1; s <= n - i; s++) printf(" ");
        for (int j = 1; j <= 2*i - 1; j++) printf("*");
        printf("\n");
    }
    // Lower half
    for (int i = n - 1; i >= 1; i--) {
        for (int s = 1; s <= n - i; s++) printf(" ");
        for (int j = 1; j <= 2*i - 1; j++) printf("*");
        printf("\n");
    }
    return 0;
}

* *** ***** ******* ***** *** *

Practice Summary

You've learned 10 patterns. Try these on your own:

#	Pattern Name	Technique
1	Right Triangle ★	j from 1 to i
2	Inverted Triangle ★	i from n down to 1
3	Square ★	j always from 1 to n
4	Hollow Rectangle ★★	border condition
5	Floyd's Triangle ★★	continuous counter num++
6	Number 1-to-i ★	print j
7	Same Number Each Row ★	print i
8	Alphabet Triangle ★★	'A' + j
9	Centered Pyramid ★★	spaces + 2i-1 stars
10	Diamond ★★★	pyramid + inverted

🏋️ More Practice Patterns

Try: (1) Right-aligned triangle (spaces on left) (2) Pascal's triangle (3) Butterfly pattern (4) X pattern (5) Checkerboard pattern (alternating * and space)

Frequently Asked Questions

How do you print patterns in C?

Patterns are printed using nested loops: an outer loop controls the rows and one or more inner loops control what is printed in each row. By adjusting how many stars, numbers or spaces the inner loop prints per row, you can build triangles, pyramids and many other shapes.

Why are nested loops used for pattern programs?

Patterns have two dimensions — rows and the items within each row — so you need two levels of looping. The outer loop moves down the rows while the inner loop fills each row, which naturally maps to the grid-like shape of most patterns.

How do you print a pyramid pattern in C?

A pyramid needs each row to print some leading spaces followed by stars, with the spaces decreasing and the stars increasing as you go down. You use one inner loop for the spaces and another for the stars, both based on the current row number.

What is the logic behind number patterns in C?

Number patterns work like star patterns but print numbers based on the row or column index instead of a fixed character. For example printing the value of the inner loop counter gives rows like 1, 12, 123, since each row prints one more number than the last.

Are pattern programs useful for learning C?

Yes. Pattern programs are a favourite practice exercise because they force you to think carefully about nested loops, counters and conditions. Mastering them builds strong control-flow skills that carry over to arrays, matrices and many other problems.

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