How to pass a variable to sprintf() function

I would like to pass a constant to sprintf() function like:

This works:

sprintf("%.2f", pi)
[1] "3.14"

Now I would like to replace 2 by a constant x say 4:

x <- 4
sprintf("%.xf", pi)

Error in sprintf("%.xf", pi) : 
  invalid format '%.x'; use format %f, %e, %g or %a for numeric objects

Expected output:

[1] "3.1416"

>Solution :

You can use an asterisk * to set the precision via argument in the format string:

x <- 4
sprintf("%.*f", x, pi)
[1] "3.1416"