Print a Hollow Alphabet Triangle Pattern in C

To print a hollow alphabet triangle pattern in C, we use nested loops to print characters in a triangular shape while ensuring that only the boundary characters and the base of the triangle are printed, leaving the inside of the triangle empty.

Examples of Hollow Alphabet Triangle Patterns

1. Basic Hollow Alphabet Triangle Pattern

In this example, we will print a hollow alphabet triangle where the first and last characters of each row are displayed, while the inside remains empty except for the last row, which is completely filled.

main.c

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#include <stdio.h>

int main() {
    int rows = 5;
    char ch = 'A';

    for (int i = 0; i < rows; i++) {
        for (int j = 0; j <= i; j++) {
            // Print character at the edges or the last row
            if (j == 0 || j == i || i == rows - 1) {
                printf("%c ", ch + j);
            } else {
                printf("  ");
            }
        }
        printf("\n");
    }

    return 0;
}

Explanation:

  1. We declare an integer variable rows to define the height of the triangle and a character variable ch initialized to 'A'.
  2. The outer for loop runs from 0 to rows - 1, representing each row.
  3. The inner for loop runs from 0 to i, printing characters based on conditions.
  4. The if condition checks if the current position is at the start, end, or last row. If true, it prints the character; otherwise, it prints a space.
  5. The character is calculated as ch + j to display increasing letters in each row.
  6. Each row ends with printf("\n") to move to the next line.

Output:

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

2. Hollow Inverted Alphabet Triangle

In this example, we will print a hollow inverted alphabet triangle where the first and last characters of each row are displayed, while the inside remains empty except for the first row, which is completely filled.

main.c

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#include <stdio.h>

int main() {
    int rows = 5;
    char ch = 'A';

    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < rows - i; j++) {
            // Print character at the edges or the first row
            if (j == 0 || j == rows - i - 1 || i == 0) {
                printf("%c ", ch + j);
            } else {
                printf("  ");
            }
        }
        printf("\n");
    }

    return 0;
}

Explanation:

  1. The variable rows defines the height of the triangle, and ch is initialized to 'A'.
  2. The outer for loop runs from 0 to rows - 1, controlling the number of rows.
  3. The inner for loop runs from 0 to rows - i - 1, decreasing in size per row.
  4. The if condition checks if the position is at the start, end, or first row and prints the character accordingly.
  5. The printed character is calculated as ch + j for increasing letters.
  6. Each row is terminated using printf("\n") to move to the next line.

Output:

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

Conclusion

In this tutorial, we explored how to print hollow alphabet triangle patterns in C:

  1. Basic Hollow Alphabet Triangle: Displays an upright triangle with hollow spaces inside.
  2. Hollow Inverted Alphabet Triangle: Prints a downward-facing triangle with boundary characters.

By using nested loops and conditional statements, we can create different variations of hollow alphabet triangles in C.