Converting R for loop to C++ equivalent in Rcpp: Expected ; after top level declarator

Question

I am fairly new learner to Rcpp, primarily needing it to speed up slow R code that is not easily parallelized because of dependencies within for loop iterations.

I wish to convert the following R code to C++ code to be directly used via Rcpp.

migrate_r <- function(pop) {
    if (m != 0) {
        if (model == "Step") {
            for (i in 1:K) {
                for (j in 1:K) {
                    for (k in 2:(K - 1)) {
                        i <- sample(perms, size = ceiling(perms * m/2), replace = FALSE)
                        j <- sample(perms, size = ceiling(perms * m/2), replace = FALSE)
                        tmp <- pop[i,, sample(k)]
                        pop[i,, sample(k)] <- pop[j,, sample(k)]
                        pop[j,, sample(k)] <- tmp
                    }
                }
            }
        }
    }
    pop
}

My attempt is as follows:

// [[Rcpp::depends(RcppArmadillo)]]
#define ARMA_DONT_PRINT_OPENMP_WARNING
#include <RcppArmadillo.h>
#include <RcppArmadilloExtensions/sample.h>
#include <set>
using namespace Rcpp;

// [[Rcpp::export]]
arma::Cube<int> migrate_cpp(arma::Cube<int> pop) {
String model;
int i, j, k, K, perms, tmp;
double m;

if (m != 0) {
    if (model == "Step") {
        for (i = 0; i < K; i++) {
            for (j = 0; j < K; j++) {
                for(k = 1; k < (K - 1); k++) {
                    i = RcppArmadillo::sample(perms, ceil(perms * m / 2), false);
                    j = RcppArmadillo::sample(perms, ceil(perms * m / 2), false);
                    tmp = pop[i, RcppArmadillo::sample(k, K, true)];
                    pop[i, RcppArmadillo::sample(k, K, true)] = pop[j, RcppArmadillo::sample(k, K, true)];
                    pop[j, RcppArmadillo::sample(k, K, true)] = tmp;
                    }
                }
            }
        }
    }
return pop;
}

Essentially both functions swap random rows in an 3-dimensional array ('pop') via a temporary variable. The C++ code doesn't run.

I know I am close to getting the C++ code to work, which will result in massive speedup compared to the R for loop.

Is there something I am missing here? Any assistance is greatly appreciated and warmly welcomed.

A reproducible example

##### Load packages #####

library(Rcpp)
library(RcppArmadillo)

### Set parameters ###

K <- 2  
N <- 6 
Hstar <- 5 
probs <- rep(1/Hstar, Hstar)
m <- 0.20
perms <- 2 # number of permutations

num.specs <- ceiling(N / K)

haps <- 1:Hstar

specs <- 1:num.specs

gen.perms <- function() {
    sample(haps, size = num.specs, replace = TRUE, prob = probs)
}

pop <- array(dim = c(perms, num.specs, K))

for (i in 1:K) {
    pop[,, i] <- replicate(perms, gen.perms())
}

pop
, , 1

     [,1] [,2] [,3]
[1,]    3    5    1
[2,]    2    3    3

, , 2

     [,1] [,2] [,3]
[1,]    2    5    3
[2,]    3    5    3

migrate_r(pop) # notice rows have been swapped between subarrays

, , 1

     [,1] [,2] [,3]
[1,]    3    5    1
[2,]    2    5    3

, , 2

     [,1] [,2] [,3]
[1,]    3    5    3
[2,]    2    3    3