How do i replace a string in text file in loop?

I need to replace a text in a notepad in loop. In the below attached file(input), the term 'zout' needs to be replace from 'zout = 0, 0.25' to 'zout = 0.25, 0.50'(and execute a bunch of other commands inside the loop) until 'zout= 28, 30'.I have attached the code(SBDRUN1) used for running the input file below.

Thanks in advance

[Bob Thompson]

You can create a new string with sprintf:

zout = sprintf('zout = %d, %d\n',var1, var2);

If this line is inside the a for loop then it will update the string with new variables each iterations. This can then be printed into the file with fprintf or a similar command.

[Vishwa Vijay]

will this replace the zout in the existing file. I need to have zout = 5,10 run one iteration and then replace it as zout=10,12 and run the loop again.

[Rik]

Unless you are using ActiveX, you can't replace text inside a file. What you can do is read the file, make the changes you want, and then writing the result to the text file, replacing it in its entirety.