How to write an easy for loop for my function in RStudio? (R script below)

I received an R script from my prof., it can convert an input adjacency matrix to a network format output. It works properly.

I'd like to write a for loop to make the file converting faster. My input files are in .csv format: ["a (1).csv", ..., "a (128).csv"]. This is my code:

for(x in 2:128)
+ {
+ convert("a (x).csv", "")
+ }
And here's the error message:

Error in file(file, "rt") : cannot open the connection In addition: Warning message:
In file(file, "rt") :
  cannot open file 'a (x).csv': No such file or directory
Could you tell me what's wrong with my code? Thanks in advance for any help!
Thank you a lot Rogojel. I've modified my codes, but it still displays an error message. What could disturb R now?

for(x in 2:128) 
convert(paste('a (', x, ').csv', sep=''), paste('a (', x, ').net', sep='') 
Error: unexpected '}' in: "convert(paste('a (', x, ').csv', sep=''), paste('a (', x, ').net', sep='') }"