You can refer below the answer to the similar question asked.
https://stackoverflow.com/questions/14096520/compile-r-script-into-standalone-exe-file
Alternatively, You can use R-shiny app for it. You can build application whih can be deployed on website also. See below link for the examples of application made by R-shiny.
https://shiny.rstudio.com/gallery/
This way client will not be seeing your code at all and will be working on it just as a tool.