Fix memory leak in for loop - c++

Question

I have issues with memory leaks on a C++ function that I have sourced into R through Rcpp. This result in a sudden abortion of my R session, without returning any specific error message.
What is weird to me is that if in function_test I move double lower =1; and double upper = value2; inside the for loop and edited them by also adding 'i': double lower =1 + i; and double upper = value2 + i; the function works without aborting my R session.
The code below is sourced in R using the function sourceCpp from Rcpp R package. I run the function with the following values:
R function:
function_test(value1=4000, value2=4000, alpha = 5e-04)
C++ code sourced in R:
// [[Rcpp::depends(RcppEigen)]]
// [[Rcpp::depends(RcppNumerical)]]
#define EIGEN_PERMANENTLY_DISABLE_STUPID_WARNINGS
#include <Eigen/Eigen>
#include <RcppNumerical.h>
#include <Rcpp.h>
using namespace Rcpp;
using namespace Numer;
// [[Rcpp::export]]
double func1(double t, double alpha, double beta){
double term1 = (( 2.0 * log(t - 0.5)) + 1) / 25.0;
int N;
if (t == 1 || t == 2) {
N = 2;
}else{
if (t <= 44) {
N = t;
}else{
N = 44;
}
}
NumericVector term_up(N);
term_up[0] = 0;
term_up[1] = term1;
double res = std::accumulate(term_up.begin(), term_up.end(), 0.0);
double int_final = (1/(25.0*t)) * (1 - (0.96)*res);
return int_final;
}
class Func1PDF: public Func
{
private:
double alpha;
double beta;
public:
Func1PDF(double alpha_, double beta_) : alpha(alpha_), beta(beta_) {}
double operator()(const double& t) const{
return func1(t, alpha, beta);
}
};
// [[Rcpp::export]]
double integrate_func(double lower, double upper, double alpha, double beta)
{
Func1PDF f(alpha, beta);
double err_est;
int err_code;
const double res = integrate(f, lower, upper, err_est, err_code);
return res;
}
// [[Rcpp::export]]
NumericVector function_test(double value1, double value2, double alpha) {
NumericVector res(value1);
double lower = 1;
double upper = value2;
for(int i=1;i<=value1;i++){
double beta = i;
res[i-1] = integrate_func(lower, upper, alpha, beta);
}
return res;
}