# Modify a value during iOS debugging in Xcode

Xcode is using the open-source [LLDB](http://lldb.llvm.org/) debugger and with the `expression` command you are able to modify a value in a running program.

![Use expression in debugger](https://cdn.hashnode.com/res/hashnode/image/upload/v1657570180267/tGB9tRiml.gif align="left")

You can verify that the value has changed with the `print` command from LLDB.

![Screen Shot 2022-07-11 at 1.15.53 PM.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1657570576694/tUuboYvPJ.png align="left")

Once you resume the program you will see that the changed value is still used.

Bonus tip 1: You can also use the abbreviation `e` as alternative to the verbose `expression` because LLDB does prefix matching. Same for `p` as alternative to `print`.

Bonus tip 2: You can use multiple expressions as actions in the Xcode debugger ti supply test/demo data. Find out more by reading [Dominik Hauser's article](https://dasdom.dev/using-breakpoints-to-populate-with-demo-data/).

![Using breakpoints to populate with demo data](https://dasdom.dev/assets/2020-01-25/breakpoint_to_populate.png)