I need to create a for, if or while loop on simulink for repetitive calculation until meeting a criterion

Hello everybody!

I need to create a loop (i guess with using for and if statements) especially on Simulink.

I have a complex setup, therefore I'll ask my question on a much simpler example.

Let's say I have a func A=x^2 ,and a desired value of it as A_reference=100

by starting from x=0, i need to find the error rate between A_reference and A_calculated and if the error rate is not smaller than a certain value,

i need to update the x and feed it to the system again, then calculate the error rate until it meets the criterion.

How can I do it on Simulink? Can you guys show me an example of it?

There are documentation of while and for iterators but I couldn't find any helpful examples..

Thanks in advance!