for loop

[Shawn Minisall]

Thanks, everyone!  Using everyone's suggestions and points, the program 
is working great now.  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,

mensanator 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
> would use xrange(1,days+1) instead.
>
> 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
>
>
>