Triangular n x n pattern program

Question

This program is supposed to print an n x n triangular pattern like this:

n = 6

* * * * * *
. * * * * *
. . * * * *
. . . * * *
. . . . * *
. . . . . *

However I am getting this:

n = 6

* * * * * *
. . . . . .
. . . . . .
. . . . . .
. . . . . .
. . . . . .

where is my mistake?

import sys

n = int(sys.argv[1])

def triangle(n):
    for i in range(n):
        if i == 0:
            for k in range(n):
                print('*', end=' ')
            print()
        if i > 0:
            for k in range(n):
                print('.', end=' ')
            print()

triangle(n)

Perhaps you should use *duck debugging*: explain your rubber duck how your program works. — Willem Van Onsem, Sep 23 '17 at 21:57
Perhaps this would help you https://stackoverflow.com/questions/26352412/python-print-a-triangular-pattern-of-asterisks — Cristian Olaru, Sep 23 '17 at 21:57

Eugene Yarmash · Answer 1 · 2017-09-24T07:35:11.517

1

Instead of checking the loop index simply use it to print the number of dots. Then print n - i stars, e.g.:

def triangle(n):
    for i in range(n):
        for k in range(i):
            print('.', end=' ')    
        for k in range(n-i):
            print('*', end=' ')
        print()

Or just using the multiplication operator:

def triangle(n):
    for i in range(n):
        print(*["."]*i + ["*"]*(n-i), sep=" ")

edited Sep 24 '17 at 07:35

answered Sep 23 '17 at 22:01

Eugene Yarmash

142,882
41
325
378

I did this and it worked, however I have a question. Why is the first for loop skipped the first time and the second one runs? – Linda Acquaviva Sep 23 '17 at 22:09
The first time it's `range(0)`, which is an empty iterator (i.e. `list(range(0)) == []`) – Eugene Yarmash Sep 23 '17 at 22:12

score 0 · Accepted Answer · answered Sep 23 '17 at 22:03

0

Currently you are printing stars only if you are on the first line and dots for every other line. You need to print dots and stars on each line increasing the number of dots and decreasing the stars:

def triangle(n):
    for i in range(n):
        for k in range(i):
            print('.', end=' ')

        for k in range(n - i):
            print('*', end=' ')

        print()

answered Sep 23 '17 at 22:03

DobromirM

2,017
2
20
29

This is exactly the same code that my (earlier) answer has. – Eugene Yarmash Sep 24 '17 at 07:33
It had a different counters in the `for` loop initially that you consequently edited and I also wanted to try and give a better explanation because you didn't have that either. – DobromirM Sep 24 '17 at 07:45

score 0 · Answer 3 · answered Sep 23 '17 at 22:17

0

Try this Its alot more simple

count = 0
count2 = 5
while count2 >= 1:
    for i in range(count):
        print(".", end = " ")
    for i in range(count2):
        print("*", end = " ")
    print()
    count = count + 1
    count2 = count2 - 1

answered Sep 23 '17 at 22:17

Kieron

21
7

Triangular n x n pattern program

3 Answers3