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I have the code here, I got the errors at n1, n2: Expression must have constant value, the value of variable "n2" cannot be used as a constant. I tried #define, delete[], const, and even std::vector but none of them worked. Are there any other ways to fix this error?

void merge(list1 arr[], int l, int m, int r)
{
     int n1 = m - l + 1;
     int n2 = r - m;

    // Create temp arrays
    list1 L[n1], R[n2];

    // Copy data to temp arrays L[] and R[]
    for (int i = 0; i < n1; i++)
        L[i] = arr[l + i];

    for (int j = 0; j < n2; j++)
        R[j] = arr[m + 1 + j];

    // Merge the temp arrays back into arr[l..r]
    // Initial index of first subarray
    int i = 0;
    // Initial index of second subarray
    int j = 0;
    // Initial index of merged subarray
    int k = l;
    while (i < n1 && j < n2) {
        if (L[i].team_1 <= R[j].team_1) { //Have to sort data based on team1
            arr[k] = L[i];
            i++;
        }
        else {
            arr[k] = R[j];
            j++;
        }
        k++;
    }
    // Copy the remaining elements of
    // L[], if there are any
    while (i < n1) {
        arr[k] = L[i];
        i++;
        k++;
    }
    // Copy the remaining elements of
    // R[], if there are any
    while (j < n2) {
        arr[k] = R[j];
        j++;
        k++;
    }
}

// l is for left index and r is
// right index of the sub-array
// of arr to be sorted */
void mergeSort(list1 arr[], int l, int r) {
    if (l >= r) {
        return;//returns recursively
    }
    int m = l + (r - l) / 2;
    mergeSort(arr, l, m);
    mergeSort(arr, m + 1, r);
    merge(arr, l, m, r);
}

enter image description here

Jack
  • 35
  • 6
  • Your compiler is absolutely correct. `list1 L[n1], R[n2];` is illegal in standard `c++` related: [https://stackoverflow.com/questions/1887097/why-arent-variable-length-arrays-part-of-the-c-standard](https://stackoverflow.com/questions/1887097/why-arent-variable-length-arrays-part-of-the-c-standard) – drescherjm Apr 12 '21 at 21:27
  • Use `std::vector L(n1), R(n2);` instead. – πάντα ῥεῖ Apr 12 '21 at 21:27
  • You're going to find that a lot in example code. Coming in from C where the VLA is legal (optional these days) I was pissed at Microsoft until I found that they'd actually followed the standard here. And after a few clients gave their systems self-induced stack overflows I came to agree with several of Microsoft's reasons for leaving it out. These days I'm pretty much anti-VLA. – user4581301 Apr 12 '21 at 22:13

0 Answers0