MATLAB/General Loops, Using a value inside a loop

Question

I'm confused on loops.

I want this MATLAB while loop to stop when the p inside the loop becomes the same as the initial p. Obviously I can't have p ~= p otherwise the loop won't start, so how would I do this as the original p is used for calculations inside the loop

e.g if p=18 I want to use that to calculate a and the next p I'll use in the while loop but I want the while loop to stop when 18 is that next p

p = input(prompt1)
q = input(prompt2)

while(??? ~= p)
    a =floor((10*p)/q)
    p= (10*p) -(an*q)
end

Answer 1

There is no p inside the loop and p outside the loop. There is only one p. If you want, set p_original = p; before the loop. Then, make the loop an infinite loop, check the condition at the end, and break out if the condition is satisfied.

p = input(prompt1);
q = input(prompt2);

p_original = p;
while 1
    a = floor((10*p)/q);
    p = (10*p) - (an*q);
    if p == p_original
        break;
    end
end

If you don't want to have that infinite loop, add a variable that keeps track of whether or not you have looped once. Inside the loop, set it to false.

first_loop = true;
while p ~= p_original | first_loop
    a = floor((10*p)/q);
    p = (10*p) - (an*q);
    first_loop = false;
end