Repeating-Letter Alphabet Triangle in C

What You’ll Learn

Row 1 is one A, row 2 is two Bs, row 3 three Cs, and so on: A, BB, CCC, DDDD, EEEEE. Contrast Program 1, where letters change inside each row. Here, the row letter stays the same and only the count grows. Next up: Program 10 reverses the letter order. Includes a live preview, worked C examples, edge cases, and complexity.

📝 Problem & Approach

Given a row count (or fixed top E), print a right-angled triangle where row k repeats the k-th letter of the alphabet k times.

// Five rows (top = E)
// A
// BB
// CCC
// DDDD
// EEEEE

Inputs & Outputs

Minimal workflow

for i from 'A' to top:          // choose the row letter
    for j from 'A' to i:        // count = row length
        print i                 // NOT j
    print newline

Approach comparison

🔮 Live Preview

Choose 1–10 rows and draw the repeating-letter alphabet triangle in the browser.

Press "Draw pattern".

Examples Gallery

Three complete C programs — fixed A–E, user-chosen row count, and a spaced-letter variant. Click View Output to reveal sample console results.

#include <stdio.h>

int main() {
    char i, j;

    for (i = 'A'; i <= 'E'; i++) {
        for (j = 'A'; j <= i; j++) {
            printf("%c", i);
        }
        printf("\n");
    }

    return 0;
}

A
BB
CCC
DDDD
EEEEE

#include <stdio.h>

int main() {
    int rows, row, col;
    char ch;

    printf("Enter the number of rows: ");
    scanf("%d", &rows);

    for (row = 1; row <= rows; row++) {
        ch = (char)('A' + row - 1);
        for (col = 1; col <= row; col++) {
            printf("%c", ch);
        }
        printf("\n");
    }

    return 0;
}

Enter the number of rows: 4
A
BB
CCC
DDDD

#include <stdio.h>

int main() {
    char i, j;

    for (i = 'A'; i <= 'E'; i++) {
        for (j = 'A'; j <= i; j++) {
            printf("%c ", i);
        }
        printf("\n");
    }

    return 0;
}

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

🔎 Worked Walkthrough — Top = E (5 rows)

Trace each row letter, how many times the inner loop runs, and the printed line.

Row lengths are 1, 2, 3, 4, 5. Every character on a row matches that row’s letter.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

For n rows you print 1+2+…+n = n(n+1)/2 characters, so total work is O(n²).

💡 Best Practices