print "This program calculates how long it takes for an investment to double in size."
print
 
investment = 1000 #initial investment
rate = input("Please enter the applicable interest rate: ") #interest rate input
years = 0 #sets years to zero
value = investment
 
while value <= investment*2: #defines loop sentinel
    value = value + value*((float(rate)/100)) #calculates investment
    years = years + 1 #adds a year for every loop
 
print "The investment doubles in",years,"years" #prints the years it took to double the investment
 
raw_input("Press enter to go on ...")  # optional console wait

print "This program calculates how long it takes for an investment to double in size."
print
 
investment = 1000
rate = input("Please enter the annual interest rate: ")
years = 0
value = investment
 
while value <= investment * 2 :
    # the next two indented lines belong to the while loop
    value = value + value * float(rate)/100
    years = years + 1
 
# this line is not part of the loop!  (not indented)
print "At", rate, "% interest your investment doubles in", years, "years"
 
raw_input("Press enter to go on ...")  # optional console wait