How do I replace on variable with another variable?

I'm working on an if statement in a for loop, and I need to replace variable 'ax' with variable 'bx' continuously throughout the whole loop...any ideas?

[Image Analyst]

Based on your other original question, you don't want to do this and should use a while loop instead of a for look like I said in your original question.

[Stephen23]

So what was wrong with the answers to your original question?:

http://www.mathworks.com/matlabcentral/answers/170816