Reverse Row Number Triangle in C

What You’ll Learn

Program 7 prints a reverse row number triangle: each row shows digits from the current row index down to 1 — 1, 21, 321, and so on. This tutorial covers the shape rule, ascending outer loop, inner countdown i..1, a live preview, worked C examples, edge cases, and complexity.

📝 Problem & Approach

Given row count rows = 5, print a reverse row number triangle — row outer index i shows digits i..1.

// rows = 5
//1
//21
//321
//4321
//54321

Inputs & Outputs

Minimal workflow

for i from 1 to rows:
    for j from i down to 1:
        print j
    print newline

Approach comparison

🔮 Live Preview

Choose a row count between 3 and 9 and draw the reverse row number triangle in the browser.

Press "Draw pattern".

Examples Gallery

Three complete C programs — fixed rows, user input, and a compact trace with rows = 3. Click View Output to reveal sample console results.

#include <stdio.h>

int main() {
    int rows = 5;
    int i, j;

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

        printf("\n");
    }

    return 0;
}

1
21
321
4321
54321

#include <stdio.h>

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

    printf("Enter the number of rows: ");
    if (scanf("%d", &rows) != 1 || rows <= 0) {
        printf("Please enter a positive integer.\n");
        return 1;
    }

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

        printf("\n");
    }

    return 0;
}

Enter the number of 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 = i; j >= 1; j--)
            printf("%d", j);

        printf("\n");
    }

    return 0;
}

1
21
321

🔎 Worked Walkthrough — rows = 5

Trace each row — outer i sets width, inner j counts down from i to 1.

Total digits printed: 1+2+3+4+5 = 15 = 5×6/2 — the fifth triangular number.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

💡 Best Practices