# for loop

Shawn Minisall trekker182 at comcast.net
Thu Oct 25 00:30:39 CEST 2007

```I agree, but if I want to get a A on the program, thats how my professor
wants the output.

:)

mensanator at aol.com wrote:
> On Oct 22, 9:12?pm, Shawn Minisall <trekker... at comcast.net> wrote:
>
>> Thanks, everyone!  Using everyone's suggestions and points, the program
>> is working great now.
>>
>
> Actually, it's not. I assume not printing the population
> was a copy error.
>
> day 1 the initial population, so if you ask for
> 8 days of multiplication, you actually only get 7.
>
> Although your code is working, it's not giving you
> the correct answer. Most of the time in these kinds
> of problems, days means elapsed days. That means for
> 100 organisms @ 25% growth/day, there will be 125
> after 1 elapsed day. But that "if (p>1):" means you
> show 100 at day 1, which is wrong. You have 100 after
> 0 elapsed days (or day 0).
>
>
>
>> Here's the updated code.
>>
>> :)
>>
>> import math
>>
>> def main():
>>     #Declare and initialize variables
>>     #starting number of organisms
>>     organisms = 0
>>     #average daily population increase as %
>>     increase = 0.0
>>     #number of days they will multiply
>>     days = 0
>>     #population prediction
>>     population = 0.0
>>
>>     #Intro
>>     print "*********************************************"
>>     print  "WELCOME TO THE POPULATION GROWTH CALCULATOR"
>>     print "*********************************************"
>>
>>     print "This program will predict the size of a population of organisms."
>>     print
>>     print
>>     while organisms <=1:
>>         organisms=input("Please enter the starting number of organisms: ")
>>         if organisms <=1:
>>             print "Error. Population must be at least two."
>>
>>     while increase <=0:
>>         increase=input("Please enter the average daily population
>> increase as a percentage (20% = .20): ")
>>         if increase <=0:
>>             print "The percent of increase must be positive."
>>
>>     while days <=0:
>>         days=input("Please enter the number of days that they will
>> multiply: ")
>>         if days <=0:
>>             print "The number of days must be positive."
>>
>>     print "         Day                                    Population"
>>     print "----------------------------------------------------------"
>>     population = organisms
>>
>>     for p in range (1,days+1):
>>         if(  p > 1 ):
>>             population = population + ( population * increase )
>>
>>         print "\t",p,
>>
>>
>>
>> mensana... at aol.com wrote:
>>
>>> On Oct 22, 5:37 pm, "mensana... at aol.com" <mensana... at aol.com> wrote:
>>>
>>>> On Oct 22, 5:22 pm, Marc 'BlackJack' Rintsch <bj_... at gmx.net> wrote:
>>>>
>>>>> On Mon, 22 Oct 2007 18:17:56 -0400, Shawn Minisall wrote:
>>>>>
>>>>>> #Intro
>>>>>>     print "*********************************************"
>>>>>>     print  "WELCOME TO THE POPULATION GROWTH CALCULATOR"
>>>>>>     print "*********************************************"
>>>>>>
>>>>>>     print "This program will predict the size of a population of organisms."
>>>>>>     print
>>>>>>     print
>>>>>>     organisms=input("Please enter the starting number of organisms: ")
>>>>>>
>>>>>>     increase=input("Please enter the average daily population increase
>>>>>> as a percentage (20% = .20): ")
>>>>>>
>>>>>>     days=input("Please enter the number of days that they will multiply: ")
>>>>>>
>>>>>> print "         Day                                    Population"
>>>>>> print "----------------------------------------------------------"
>>>>>>
>>>>>> for p in range (days):
>>>>>>
>>>>>>     population = organisms * population * increase
>>>>>>
>>>>>>     print days,
>>>>>>
>>>>>>     print "\t\t\t\t",population
>>>>>>
>>>>>> I'm having problems with my for loop here to calculate estimated
>>>>>> population output to a table.  Instead of knowing how much I want to
>>>>>> loop it, the loop index is going to be whatever number of days the user
>>>>>> enters.  When I run my program, it asks the 3 questions above but then
>>>>>> just dead stops at a prompt which leads me to believe there's something
>>>>>> wrong with my loop.
>>>>>>
>>>>> It should not run at all as it is indented inconsistently.  If that
>>>>> problem is corrected it will stop with a `NameError` because you try to
>>>>> read `population` before anything was assigned to it.
>>>>>
>>>>> Ciao,
>>>>>         Marc 'BlackJack' Rintsch
>>>>>
>>>> Also, I would guess that you want to print p, not days
>>>>
>>> Oh, and your calculation is incorrect. You don't multiply by
>>> organisms in every loop iteration, organisms is the initial
>>> value of population, so you can solve the "Name" error by doing
>>> population = organisms before the for..loop.
>>>
>>> And since you're asking for an increase, you don't multiply by the
>>> percent (as that would decrease the population), but instead by
>>> 1+increase.
>>>
>>> Also, does day==0 represent the first day of increase or the
>>> initial value? One would normally expect day==0 to be the initial
>>> value, but as written, day==0 is the first day of increase. I
>>>
>>> Lastly, you can't have a fraction of an organism, right? You might
>>> want to print your floating point population rounded to an integer.
>>>
>>> population = organisms
>>> for p in xrange(1,days+1):
>>>   population = population * (1 + increase)
>>>   print p,
>>>   print "\t\t\t\t%0.0f" % (population)
>>>
>>> ##  *********************************************
>>> ##  WELCOME TO THE POPULATION GROWTH CALCULATOR
>>> ##  *********************************************
>>> ##  This program will predict the size of a population of organisms.
>>> ##
>>> ##
>>> ##  Please enter the starting number of organisms: 100
>>> ##  Please enter the average daily population increase as a percentage
>>> (20% = .20): 0.25
>>> ##  Please enter the number of days that they will multiply: 8
>>> ##           Day                                    Population
>>> ##  ----------------------------------------------------------
>>> ##  1                              125
>>> ##  2                              156
>>> ##  3                              195
>>> ##  4                              244
>>> ##  5                              305
>>> ##  6                              381
>>> ##  7                              477
>>> ##  8                              596- Hide quoted text -
>>>
>> - Show quoted text -
>>
>
>
>

```