[Tutor] Loop help

[Dave Angel]

Nathan Wing wrote:
> Hello All,I've been racking my brain trying to figure out, what I imagine to
> be, a very simple problem.  I found the Intro to comp science MIT open
> course (
> http://ocw.mit.edu/OcwWeb/Electrical-Engineering-and-Computer-Science/6-00Fall-2007/CourseHome/index.htm)
> and was working on the very first homework assignment.  I was successful in
> problem one, but having a hard time with problem two.  Any help would be
> greatly appreciated!
>
> Regards,
> Nathan
>
> Here is the problem:
>
> A wealthy donor has given MIT $500,000 to be used to pay the tuition of one
> student every other year until the money runs out. Under the assumptions
> that
> a. The current annual tuition is $34,986 per year,
> b. Tuition goes up at a rate of 4.1%/year, and
> c. The principal will be invested so that it earns 5%/year,
>
> solve the following problems:
> 1) Write a program that calculates and prints the total number of students
> this gift will support and the tuition paid for the last student.
> 2)Write a program that calculates and prints the smallest gift (rounded to
> the nearest $100) needed to support one student every other year for 100
> years. In addition, print the number of iterations your program took to
> arrive at the answer. Hint: you may want to use nested loops for this
> problem.
>
> my code that works for number 1:
>
> #!/usr/bin/env python
> #
> #scholarship.py
> #
>
> #initialize values
> year = 0
> count = 0
> money = 1000000.0 #fund amount
> ctuition = 34986.0 #current tuition
> rate = 1.041 # 4.1% annual increase on tuition
> principle = 1.05 #5% annual interest accrued on fund
>
> ###calculations
> while money > 0 and money >= ctuition: #while the fund has money and can
> cover tuition
>     if year % 2 == 0: #if this is year 0 or every even year after year 0
>         money = money - ctuition
>         ftuition = ctuition
>         count += 1
>
>     ctuition = ctuition * rate
>     money = money * principle
>     year += 1
>
> print "Total number of students aided: %d" % count
> print "Tuition paid for final recipient: $%.2f" % ftuition
> print 'Total number of years fund was operative: %s' % str(year + 1)
>
>
> my code for number two (this code ends up looping and does not increment the
> initial funding, as I had thought it would):
>
> #!/usr/bin/env python
> #
> #scholarship2.py
> #
>
> ###  initialize values
>
> loop = 1
> while loop is 1:
>
>     year = 0
>     count = 0
>     initmoney = 500000.0 #initial funding
>     money = initmoney #fund amount
>     ctuition = 34986.0 #current tuition
>     rate = 1.041 # 4.1% annual increase on tuition
>     principle = 1.05 #5% annual interest accrued on fund
>
>
> ###  calculations
>     while money > 0 and money >= ctuition: # while the fund has money and
> can cover tuition
>         if year % 2 == 0: # if this is year 0 or every even year after year
> 0
>             money = money - ctuition
>             ftuition = ctuition
>             count += 1
>             print "pass ", count
>
>         ctuition = ctuition * rate
>         money = money * principle
>         year += 1
>
>     if year == 100:
>         loop = 0
>         print "The total funding required to last 100 yrs: $%.2f" %
> initmoney
>         print count
>         print year
>     else:
>         print 'restart with new funding'
>         initmoney += 100.0
>         year = 0
>         count = 0
>         ctuition = 34986.0
>
>   
This isn't your only problem, but the immediate difficulty you mention, 
the incorrect value for initmoney, is caused by initializing said value 
inside the while loop.  Thus every time you go through the while loop, 
it will be set to the same value.  Since you want to increment it by 
100, you need to move the initialization outside of the loop:

initmoney = 500000.0 #initial funding

loop = 1

while loop == 1:

    year = 0
    count = 0
    money = initmoney #fund amount
    ...

I think I'd also eliminate the loop variable in favor of a "break" statement.  Make it a while True, and use break when you print out the result.

DaveA