Not expected output shown

Question

n=8
list=[3,21,5,6,14,8,14,3]

#expected output=[3,5,21,6,8,14,3,14]
for i in range (0,n-1,1):
if list[i]%7==0:
list[i],list[i+1]=list[i+1],list[i]
i=i+1
print(list)

Answer 1

A for...loop uses a fixed range and stepping, but in this case we have to adjust the loop counter <i> sometimes only, not always. That happens when element at index <i> is multiple of 7. A while...loop is more suitable IMHO when we need to adjust loop counter in various ways, maybe even with different stepping values.

Answer 2

Bob
Yes you got it right man!
While...loop allows us to change loop counter arbitrarily, for...loop in other language also supports loop counter modification; but it seems not the case in Python, cmiiw

Answer 3

As per given expected output it is not clear what you want.

Answer 4

Because the loop counter (index) needs adjustment when an element at the said index is fully divisible by 7. Otherwise I'd be swapping elements at the unintended index next time around.

Answer 5

Thanks a ton Ipang

Answer 6

Ok so what I'm seeing is if list[n] is a multiple of seven, have it swap places with list[n+1] and increase the loop counter by 2, otherwise do nothing and increase counter by 1. Do I have it right?

Answer 7

Bob
That's right!

If element[ i ] is multiple of seven then we swap element value with the next one ( element [ i + 1 ] ), and increment <i> because we want to skip element[ i + 1 ] next time around.

We rather want to continue checking multiples of 7 again from element[ i + 2 ] because element [ i ] and element [ i + 1 ] had already been swapped, no need for a re-check.

Answer 8

Ok, assuming I have it right, the i+=1 in your if statement is a different i than the iterator. The iterator can't(easily) be modified in the body of a for loop. If you need the iterator to change by a different amount based on a condition, then you have to use a while loop

Answer 9

Remember this is a QUESTION and answer section. So what exactly is your question and the issue you are facing?

Answer 10

Justice I have already mentioned expected output

Answer 11

Atul [Inactive] But you don't state the actual output. It's always best to share your code via codebits so that we don't try and guess.

Answer 12

A͢J Justice just run the above code in code playground and find the difference between the outputs and fix the error

Answer 13

Atul [Inactive] Or! Since you are the one asking for help, you can adjust your post to make it easier for others to help instead of making not just me or A͢J, but anyone interested in helping you that sees this question, do the work instead.

Answer 14

Ok Justice I will make it sure next time

Answer 15

https://code.sololearn.com/cAV79x8kKEoQ/?ref=app

Answer 16

Atul [Inactive] Can you explain what you want your algorithm to do exactly (not just the output). Also, how have you tried debugging this?

Answer 17

The question is swap the next value divisible by 7

Answer 18

Atul [Inactive] I would suggest adding some print statements to see what your code is doing. You can put one right before the conditional (if statement) as well as printing out what you presume to be swapping.

Answer 19

We need to adjust value of <i> when <i> is fully divisible by 7. I think use of while...loop is preferable in this case. We're not supposed to alter a for...loop counter, we use while...loop when we need to.

lst=[ 3, 21, 5, 6, 14, 8, 14, 3 ]
n = len( lst )
#expected output=[3,5,21,6,8,14,3,14]
i = 0
while i < n - 1:
if lst[ i ] % 7 == 0:
lst[ i ], lst[ i + 1 ] = lst[ i + 1], lst[ i ]
i += 1
i += 1
print( lst )

P.S. I would suggest you not to use keywords for variable names, like `list`. You will overwrite `list` definition and confuse yourself in bigger codes/projects when you need to use the original `list` keywords.

Answer 20

Ipang why u have written i+=1 two times ?And why only i+=1 when it is doing the work of skipping the next number?