Repeating Number Triangle in C

What You’ll Learn

Program 9 prints a repeating number triangle: each row repeats the row digit i exactly i times — 1, 22, 333, and so on. This tutorial covers the shape rule, outer loop for the digit, inner loop for repetition, a live preview, worked C examples, edge cases, and complexity.

📝 Problem & Approach

Given row count rows = 5, print a repeating number triangle — row i shows digit i repeated i times.

// rows = 5
//1
//22
//333
//4444
//55555

Inputs & Outputs

Minimal workflow

for i from 1 to rows:
    repeat i times:
        print i
    print newline

Approach comparison

🔮 Live Preview

Choose a row count between 3 and 9 and draw the repeating 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 = 1; j <= i; j++)
            printf("%d", i);

        printf("\n");
    }

    return 0;
}

1
22
333
4444
55555

#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 = 1; j <= i; j++)
            printf("%d", i);

        printf("\n");
    }

    return 0;
}

Enter the number of rows: 4
1
22
333
4444

#include <stdio.h>

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

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

        printf("\n");
    }

    return 0;
}

1
22
333

🔎 Worked Walkthrough — rows = 5

Trace each row — outer i is the digit, inner j counts repetitions from 1 to i.

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