Putting a loop in a function

I'm stuck here. The following code works great if I just use it on the
command line in a 'for' loop. Once I try to define it as a function as
seen
below, I get bad results. I'm trying to return a vector of column indices
based on a short string that is contained in a selection (length of about
70) of long column names that changes from time to time. Is there an
existing function that will do this for me? The more I think about this
problem, the more I feel there has to be a function out there. I've not
found it.


ind <- function(col, string, vector){  # this is really the problem. I
don't
feel like I'm declaring these arguments properly.
  indices <- vector(mode = 'numeric') # I am not entirely confident
that
this use is necessary. Is indices <- c() okay?
  for (i in 1:length(col)){
    num <- regexpr(str, col[i])
    if (num != -1){
         indices <- c(vector, i) # I've also had success with indices
<-
append(indices, i)
  }
}
indices
}

ind(d[,'Column.I.want'], 'string', 'output.vector')

Am I wrong here? I've read that the last statement in the function is what
it will return, and what I want is a vector of integers.