Segmentation fault:11 MergeSort - c++

Question

I try to implement the merge sort algorithm and I get a segmentation fault. Why? The error seems to be in the MergeSort function. The merge sort function (on the 2nd call) when should check only an array of 4 numbers (the length should be 4) shows the length = 27. Why? (tested on an array with 8 elements)
#include<iostream>
using namespace std;
int n, A[1000];
void citire(int lungime) {
for (int i = 0; i < lungime; i++) cin >> A[i];
}
void afisare(int lungime) {
for (int i = 0; i < lungime; i++)
cout << A[i] << " ";
cout << '\n';
}
int lungime(int A[]) {
int i = 0;
while (A[i]) i++;
return i;
}
void Merge(int L[], int R[], int A[]) {
int nL = lungime(L);
int nR = lungime(R);
int i = 0, j = 0, k = 0;
while (i < nL && j < nR) {
if (L[i] <= R[j]) {
A[k] = L[i];
i++;
}
else {
A[k] = R[j];
j++;
}
k++;
}
while (i < nL) {
A[k] = L[i];
i++;
k++;
}
while (j < nR) {
A[k] = R[j];
j++;
k++;
}
}
void MergeSort(int A[]) {
int n1 = lungime(A);
if (n1 < 2) return;
else
{
int mid = (int)n1 / 2;
int L[mid];
int R[n - mid];
for (int i = 0; i < mid; i++)
L[i] = A[i];
for (int i = mid; i < n; i++)
R[i - mid] = A[i];
MergeSort(L);
MergeSort(R);
Merge(L, R, A);
}
}
int main() {
cin >> n;
citire(n);
MergeSort(A);
afisare(n);
return 0;
}

Answer 1

Changes made in this example. A[], L[], R[] are allocated using new. A[] is passed as a parameter. L[] and R[] are allocated in Merge(). Size and/or indices passed as parameters, and lungime() is no longer used to get size. Other changes noted in comments.
#include<iostream>
using namespace std;
void citire(int A[], int lungime) { // A is parameter
for (int i = 0; i < lungime; i++) cin >> A[i];
}
void afisare(int A[], int lungime) { // A is parameter
for (int i = 0; i < lungime; i++)
cout << A[i] << " ";
cout << '\n';
}
// A, low, mid, end are parameters
// L and R allocated here
void Merge(int A[], int low, int mid, int end) {
int sizeL = mid-low;
int sizeR = end-mid;
int *L = new int[sizeL];
int *R = new int[sizeR];
for(int i = 0; i < sizeL; i++)
L[i] = A[low+i]; // A[low+i]
for(int i = 0; i < sizeR; i++)
R[i] = A[mid+i]; // A[mid+i]
int i = 0, j = 0, k = low; // k = low
while (i < sizeL && j < sizeR) {
if (L[i] <= R[j]) {
A[k] = L[i];
i++;
}
else {
A[k] = R[j];
j++;
}
k++;
}
while (i < sizeL) {
A[k] = L[i];
i++;
k++;
}
while (j < sizeR) {
A[k] = R[j];
j++;
k++;
}
delete[] R;
delete[] L;
}
// A, low, end are parameters
void MergeSort(int A[], int low, int end) {
int sizeA = end - low;
if(sizeA < 2)
return;
int mid = low + (sizeA / 2); // mid = low + ...
MergeSort(A, low, mid);
MergeSort(A, mid, end);
Merge(A, low, mid, end);
}
int main() {
int n;
cin >> n;
int *A = new int[n]; // A is allocated
citire(A, n); // A, n are parameters
MergeSort(A, 0, n); // A, 0, n are parameters
afisare(A, n); // A, n are parameters
delete[] A;
return 0;
}

Answer 2

"The lungime function is the length of the string and this function works good. I've tested it on different arrays".
Well, this is purely accidental; uninitialized memory can contain zeros, and provide the array terminator by accident.
If you want to keep the current design, you should:
initialize A to zeros
make sure that there are no more than 999 elements in the input stream,
that no element has the value zero, as zero is reserved, and used as terminator, and
define L and R (in MergeSort) one element longer, and initialize the last element to zero.
Unless there are overwhelming reasons for a "roll your own" sort solution, you might have a look at prefab sort support. The vector class in C++ offers just that.