Problems with while expression in a script

disp('This program will calculate the number of years required for a savings account earning 5% annual interest to reach target value.')

I = input('Please enter the intial ammount put in the account: ');

T = input('Please enter the target ammount for the account: ');
Y=0;

%Expression:
while T ~= I*(1.05^Y)
  Y = Y+1;
end

fprintf('It will take %i years to save up for your target ammount.',Y)

The one thing I have a problem with is that it only works for very small numbers such as it taking one year to go from 1 to 1.05 or 2 years from 1 to 1.1025. Also, I want to make it have a message telling the user to re enter values if the target value is less than the initial value.

[Andreas Goser]

I posted a suggestion to your first question. Can you test this and then re-consider / edit this one?

Answer 1

[Walter Roberson]

Please see this FAQ

Answer 2

[Matt Fig]

As Walter intimates, this is a floating point issue. Instead of using a tolerance, you might want to think about the problem at hand. For example:

while T - I*(1.05^Y)>0
  Y = Y+1;
end

Of course you should also put a check in your code which insures (or errors when appropriate) that T>I initially.