Right-Aligned Descending Number Triangle in C

What You’ll Learn

The right-aligned descending triangle prints 1, 21, 321, 4321, 54321 — a natural step after the spaced mirror in Program 29. This tutorial covers fixed-width loops, leading-space padding, conditional printing, a live preview, worked C examples, edge cases, and complexity.

📝 Problem & Approach

Given rows = 5, print a right-aligned descending triangle: for each i, print spaces while j > i, then print digits i..1 in a fixed-width inner loop.

// rows = 5 (conceptual shape)
//     1
//    21
//   321
//  4321
// 54321

Inputs & Outputs

Minimal workflow

for i from 1 to rows:
    for j from rows down to 1:
        if j > i: print space
        else: print j
    print newline

Approach comparison

🔮 Live Preview

Choose a row count between 3 and 9 and draw the right-aligned descending triangle in the browser.

Press "Draw pattern".

Examples Gallery

Three complete C programs — fixed rows, user input with ternary form, and a smaller trace demo. Click View Output to reveal sample console results.

#include <stdio.h>

int main() {
    int i, j;

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

    return 0;
}

    1
   21
  321
 4321
54321

#include <stdio.h>

int main() {
    int rows;
    int i, j;

    printf("Enter rows: ");
    scanf("%d", &rows);
    if (rows < 1) return 0;

    for (i = 1; i <= rows; ++i) {
        for (j = rows; j >= 1; --j)
            (j > i) ? printf(" ") : printf("%d", j);

        printf("\n");
    }

    return 0;
}

Enter rows: 4
   1
  21
 321
4321

#include <stdio.h>

int main() {
    int rows = 3;
    int i, j;

    for (i = 1; i <= rows; ++i) {
        for (j = rows; j >= 1; --j) {
            if (j > i) printf(" ");
            else printf("%d", j);
        }
        printf("\n");
    }

    return 0;
}

  1
 21
321

🔎 Worked Walkthrough — rows = 5

Trace each outer-loop value of i, leading-space count, digit range, and full row output.

Leading spaces per row = rows - i — zero when i = rows.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

💡 Best Practices