Implementation of merge sort in c++

mergesort.cpp

// Declare/initialize any useful variables here, including the temporary array 
// to merge values into and then copy back into the parameter array.

/*
while the temporary array is not filled
if there are no more values in the left part of a,
move next value from right part of a into next index of the temporary array otherwise, if there are no more values in the right part of a,
move next value from left part of a into next index of the temporary array otherwise (values in each part) compare the first value in each part
move smallest value from a into next index of the temporary array
Copy all values from the temporary array back into a, starting at left_low
*/

void merge_sort(int a[], int length) {
    merge_sort(a, 0, length-1);
}

void merge_sort(int a[], int low, int high) {
    if (low >= high)                  //Base case: 1 value to sort->sorted
      return;                         //(0 possible only on initial call)
    else {
      int mid = (low + high)/2;       //Approximate midpoint*
      merge_sort(a, low, mid);        //Sort low to mid part of array
      merge_sort(a, mid+1, high);     //Sort mid+1 to high part of array
      merge(a, low, mid, mid+1,high); //Merge sorted subparts of array
    }
}

void merge(int a[], int left_low, int left_high, int right_low, int right_high) 
{ 
    int length = right_high-left_low+1;
    int temp[length];
    int left = left_low;
    int right = right_low;
    for (int i = 0; i < length; ++i) { 
        if (left > left_high)
            temp[i] = a[right++];
        else if (right > right_high)
            temp[i] = a[left++];
        else if (a[left] <= a[right])
            temp[i] = a[left++];
        else
            temp[i] = a[right++]; 
    }
    
    for (int i=0; i< length; ++i) 
        a[left_low++] = temp[i];
}

very efficient 👍 but there minor observation in Merge() function you cant just declare an array on int with variable int temp[length];
i think you should invoke it in the heap then delete it at the end should be like int* temp = new int [length];
then at the end of the function
delete temp;
thank you the code is very elegant and very helpful with all those comments 💯

very efficient but there minor observation in Merge() function you cant just declare an array on int with variable int temp[length];
i think you should invoke it in the heap then delete it at the end should be like int* temp = new int [length];
then at the end of the function
delete temp;

Don't forget the brackets on your delete
delete[] temp;