How to compare previous iteration output with current iteration output?

I have a program with for loop having 1to 500. I need to compare the output of previous and current iteration, if the outputs are matching the program has to stop. Otherwise the loop has to continue till the match is achieved.

Answer 1

[Torsten]

xold = 2;
error = 1;
while error > 1e-6
    x = xold - (xold^2-2)/(2*xold);
    error = abs(x-xold);
    xold = x;
end
x

x = 1.4142