How do I use a C algorithm in shinyR

My basic aim of the code is to input 4 text files, that should be processed by a C algorithm to return a table output. I am confused as to how to make sure that the files the user inputs will be processed by the algorithm.

server <- function(input, output) {
output$contents5 <- renderTable({


Could someone please help me with this.

You should first put aside the question of shiny and establish that you can apply your C algorithm in a non shiny script. I would use the Rcpp package.