An ascending number triangle grows one digit per row: row i prints digits 1 through i.
Rule: on row i, print j for j = 1..i
1
12
123
1234
12345 ← rows = 5Follows the left-aligned descending triangle in Program 4; next is the reverse ascending triangle in Program 6.
Outer loop picks row i from 1 to rows. Inner loop prints digits 1..i.
| Method | Idea | Best for |
|---|---|---|
| Tight digits | print(j, end="") with no spaces | Learning, interviews, exams |
| Spaced digits | print(j, end=" ") | Easier reading / wider values |
for i from 1 to rows:
for j from 1 to i:
print j (no newline)
print newline| Goal | Pattern |
|---|---|
| Walk rows | for i in range(1, rows + 1): |
| Walk digits | for j in range(1, i + 1): |
| Print digit | print(j, end="") |
| Spaced digit | print(j, end=" ") |
| End the row | print() |
| API | Effect | Use for |
|---|---|---|
print(j, end="") | Stays on the same line | Each digit |
print() | Ends the current line | After the inner loop finishes a row |
Print digits without a newline, then end the row once. Putting bare print() inside the inner loop turns the triangle into a vertical list.
Change the row count and the ascending triangle updates instantly.
i = 4Trace four digits glued together as 1234.
j | Line so far | |
|---|---|---|
1 | 1 | 1 |
2 | 2 | 12 |
3 | 3 | 123 |
4 | 4 | 1234 |
After j finishes, bare print() starts the next row. Row 5 will print one more digit — 12345.
Three complete programs: fixed rows = 5, input() rows, and spaced digits. Use View Output to reveal sample results.
rows = 5Hard-coded height — outer loop grows the row, inner loop prints 1..i.
rows = 5
for i in range(1, rows + 1):
for j in range(1, i + 1):
print(j, end="")
print()1. Outer loop grows. i runs from 1 to 5 — each value is one row.
2. Inner loop prints 1..i. j runs from 1 to i; each digit uses print(j, end="").
3. Newline. Bare print() runs only after the inner loop finishes.
Read the row count with input() and build the same triangle.
try:
rows = int(input("Enter the number of rows: "))
except ValueError:
print("Please enter a positive integer.")
raise SystemExit(1)
if rows < 1:
print("Please enter a positive integer.")
raise SystemExit(1)
for i in range(1, rows + 1):
for j in range(1, i + 1):
print(j, end="")
print()1. Validate rows. Catch ValueError; require rows >= 1.
2. Same triangle. Only the bound changes from the literal 5 to the user value.
3. Safer input tip. Cap demos for readable output:
if rows < 1 or rows > 9:
print("Enter a whole number from 1 to 9.")
raise SystemExit(1)Same loops — add a space after each digit for easier reading.
rows = 5
for i in range(1, rows + 1):
for j in range(1, i + 1):
print(j, end=" ")
print()1. Only the print changes. print(j, end=" ") instead of print(j, end="").
2. Same bounds. Outer and inner limits match Example 1 exactly.
3. Useful for wider values. Spaces keep multi-digit numbers readable when rows grows.
Check these before calling the solution done.
print() inside the inner loopThat prints one digit per line. Call bare print() only after the inner loop.
end=""Default print(j) puts each digit on its own line. Use end="" (or end=" ") inside the row.
print()Without it, every digit glues onto one endless line.
You get Program 1’s shrinking triangle (12345, 1234, …). Keep i from 1 up to rows.
Output is just 1. A good sanity check for input validation.
ValueErrorBare int(input()) crashes on non-numeric text — wrap it in try/except ValueError.
| Program | Time | Extra space |
|---|---|---|
| Nested loops (Examples 1–3) | O(n²) | O(1) |
Total prints are 1 + 2 + … + n = n(n + 1) / 2 — quadratic in n.
i, print j for j = 1..i.print() only after the inner loop.O(n²) time; O(1) extra space.One line: for each row i from 1 to rows, print digits 1..i, then end the line.
Row i prints digits 1 through i. The outer loop counts up from 1 to rows, so each row grows by one digit — total prints = n(n+1)/2, time O(n²).
Continue with a related ascending pattern that reverses each row.
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