A shrinking repeating number pattern prints digit i repeated rows - i + 1 times, counting i up from 1 so each row gets shorter.
Remember
Rule: for i = 1..n, print i exactly (n - i + 1) times
11111
2222
333
44
5 ← 5 rows
In C you solve it with two nested for loops: the outer loop picks the digit, the inner loop runs from i to rows with printf("%d", i), then printf("\n") ends the row. Program 11 is the inverted twin (55555, 4444, 333…).
Approach
How to Solve It
Outer loop counts up from 1 to rows. Inner loop runs from i to rows so width shrinks. End each row with printf("\n").
Method
Idea
Best for
Nested loops
Outer picks digit 1..n; inner runs i..n so width shrinks
Learning, interviews, exams
putchar
Write each repeated digit without a format string
Leaner demos once loops click
Pseudocode
Pseudocode
for i from 1 to rows:
for j from i to rows:
print i (no newline)
print newline
Cheat sheet
Goal
Pattern
Pick digit (count up)
for (i = 1; i <= rows; i++)
Shrink repeats
for (j = i; j <= rows; j++) printf("%d", i);
End the row
printf("\n");
putchar form
putchar('0' + i); inside the same inner loop
Inverted twin (Program 11)
for (i = rows; i >= 1; i--) with printf("%d", i) × i
Printing Numbers vs Starting a New Line
API
Effect
Use for
printf("%d", i)
Stays on the same line
Each repeat of digit i
printf("\n")
Ends the current line
After the inner loop
Print all repeats without a newline, then end the row once.
Try it
Live Preview
Change the row count and the shrinking pattern updates instantly — capped at 9 so every digit stays a single character.
Whole numbers from 1 to 9 (single digits). Tap a chip or type a value — the preview redraws as you go.
Live result5 rows · 15 digits
11111
2222
333
44
5
Trace
Worked Walkthrough — rows = 4
Trace each outer-loop value of i, how many times the inner loop runs, and the printed row.
i
Inner j
Repeats
Printed row
1
1..4
4
1111
2
2..4
3
222
3
3..4
2
33
4
4..4
1
4
Total digits are 4+3+2+1 = 10 — the triangular number n(n+1)/2.
Code
C Programs
Three complete programs: fixed height, scanf input, and a putchar shortcut. Use View Output for sample results.
Example 1 — Fixed rows = 5
Outer loop counts up; inner loop runs from i to rows so each row shrinks.
C
#include <stdio.h>
int main(void)
{
int rows = 5;
int i, j;
for (i = 1; i <= rows; i++)
{
for (j = i; j <= rows; j++)
printf("%d", i);
printf("\n");
}
return 0;
}
Output
11111
2222
333
44
5
How It Works
1. Count up.for (i = 1; i <= rows; i++) yields 1, 2, 3, 4, 5 — the digit for each row.
2. Shrink width. When i = 1, the inner loop runs five times (11111); when i = 5, just once (5).
3. Newline.printf("\n") after the inner loop starts the next shorter row.
Example 2 — User Input
Read the row count with scanf and reject non-positive values.
C
#include <stdio.h>
int main(void)
{
int rows;
int i, j;
printf("Enter the number of rows: ");
if (scanf("%d", &rows) != 1 || rows < 1)
{
printf("Please enter a positive integer.\n");
return 1;
}
for (i = 1; i <= rows; i++)
{
for (j = i; j <= rows; j++)
printf("%d", i);
printf("\n");
}
return 0;
}
Output (when user enters 4)
Enter the number of rows: 4
1111
222
33
4
How It Works
1. Validate rows. Require scanf success and rows >= 1.
2. Same nested loops. Four rows start at 1111 and end at 4.
3. Safer demos. Cap at single-digit rows if you want a tight look:
Safer input
if (scanf("%d", &rows) != 1 || rows < 1 || rows > 9)
{
printf("Enter a whole number from 1 to 9.\n");
return 1;
}
Example 3 — putchar Shortcut
Same loops with putchar('0' + i) — best for single-digit rows (1–9).
C
#include <stdio.h>
int main(void)
{
int rows = 5;
int i, j;
for (i = 1; i <= rows; i++)
{
for (j = i; j <= rows; j++)
putchar('0' + i);
putchar('\n');
}
return 0;
}
Output
11111
2222
333
44
5
How It Works
1. Digit as char.'0' + i maps 1..9 to characters '1'..'9'.
2. Same shape. Identical output to Example 1 — keep the printf version for exams that expect format strings.
Edge Cases & Pitfalls
Check these before calling the solution done.
wrong twin
for (j = 1; j <= i; j++)
That grows repeats (1, 22, 333 — Program 9). Keep j from i to rows so width shrinks.
\n inside
printf("\n") inside the inner loop
That puts each digit on its own line. Print repeats without a newline; call printf("\n") only after the row finishes.
wrong start
j = 1 instead of j = i
Starting at 1 every time makes every row length rows — you get a rectangle, not a shrinking triangle.
rows = 1
Single digit
Output is just 1 — a good sanity check.
rows ≤ 0
Empty output
The outer loop never runs. Validate and prompt again for clearer UX.
multi-digit
rows > 9
printf("%d", 10) prints two characters. Labs usually stick to 1–9; putchar('0' + i) also assumes a single digit.
Analysis
Time and Space Complexity
Program
Time
Extra space
Nested loops (Examples 1–2)
O(n²)
O(1)
putchar shortcut (Example 3)
O(n²)
O(1)
There are n rows printing n+(n-1)+…+1 digits, so total work is n(n+1)/2.
Remember
Key Takeaways
Rule: for i = 1..n, print digit i exactly n - i + 1 times.
Inner bound:j from i to rows shrinks the width as the digit grows.
printf vs newline: repeats stay on the line; printf("\n") advances after each row.
Next step: Program 13 introduces alternating rows.
One line: for each digit from 1 to n, print it n-i+1 times with printf, then printf("\n").
Frequently Asked Questions
The inner loop runs from j = i to rows. As i increases (1, 2, 3, …), the inner loop runs fewer times, so each row prints fewer copies of the row digit.
On the first row, i = 1 and the inner loop runs from 1 to rows, so it prints 1 exactly rows times — five 1s when rows = 5.
printf("%d", i) stays on the same line. printf("\n") ends the current line. Repeated digits use printf; the row break uses printf("\n") after the inner loop.
Use the inner loop as 1..i instead of i..rows so the repeat count grows (see Program 9).
Program 11 counts the outer loop down and repeats digit i exactly i times (55555, 4444, 333, 22, 1). Program 12 counts up and uses for (j = i; j <= rows; j++) so digit i repeats rows - i + 1 times (11111, 2222, 333, 44, 5).
O(n²) where n is the number of rows. Total digit prints equal n+(n-1)+…+1 = n(n+1)/2.
Yes. putchar('0' + i) writes one digit when i is 1..9. Nested loops with printf are better for learning; putchar is a leaner shortcut once the bounds make sense.
Check scanf's return value: if (scanf("%d", &rows) != 1) handle bad input. Unchecked scanf leaves rows uninitialized on failure.
The outer loop never runs, so nothing is printed. Validate and prompt again if you want a clear user message.
🤔
Did you know?
Row digit i repeats rows − i + 1 times. The outer loop counts up from 1, while the inner loop starts at i and runs to rows, so each row shrinks — still O(n²) total prints.
