Errors Within Void Merge - c++

Question

I've been having problems trying to figure out how to fix this code I wrote for Mergesort.
The intended result was to output a sorted array of inputs, but the void merge function contains errors that result in either an unsorted array or an array of really large or small numbers.
I've tried many times to fix them, but the result still doesn't come out perfectly.
Can you look it over and tell me what I've been doing wrong?
#include "pch.h"
#include <iostream>
using namespace std;
void merge(int* arr, int p, int q, int r) {
//copy A[p.q] into L
//and A[q+1.r] into R
int i, j, k;
int n1 = q - p + 1;
int n2 = r - q;
int* L = new int[n1+1];
int* R = new int[n2+1];
for (i = 1; i <= n1; i++) {
L[i] = arr[p+i-1];
}
for (j = 1; j <= n2; j++){
R[j] = arr[q+j];
}
L[n1+1] = 99999;
R[n2+1] = 99999; //represents infinity
i = j = 1;
for (k = p; k <= r; k++)
{
if (L[i] <= R[j]) {
arr[k] = L[i];
i = i + 1;
}
else {
arr[k] = R[j];
j = j + 1;
}
return;
}
}
void mergesort(int* arr, int p, int r) {
if (p < r) {
int q = floor((p + r) / 2);
mergesort(arr, p, q);
mergesort(arr, q + 1, r);
merge(arr, p, q, r);
}
return;
}
int main() {
int r;
cin >> r;
int* arr = new int[r];
for (int i = 0; i < r; i++) {
int num;
cin >> num;
arr[i] = num;
}
int p = 0;
//sortint function
mergesort(arr,p,r);
for (int i = 0; i < r; i++) {
cout << arr[i] << ";";
}
return 0;
}