#include<iostream>
using namespace std;

void mergeArrays(int x[],int y[],int a[],int s,int e){
       int mid = (s+e)/2;
       int i=s;
       int j = mid+1;
       int k = s;
       while(i<=mid && j<=e){
           if(x[i] < y[j]){
            a[k] = x[i];
            i++;
            k++;
           }else{
             a[k] = y[j];
             j++;
             k++;
           }
       }
       while(i<=mid){
        a[k] = x[i];
        k++;
        i++;
       }
       while(j<=e){
        a[k] = y[j];
        k++;
        j++;
       }
}

void mergeSort(int a[],int s,int e){
    if(s>=e){
        return;
    }
    int mid = (s+e)/2;
    int x[100],y[100];
    for(int i=s;i<=mid;i++){ 
        x[i] = a[i];
    }
    for(int i=mid+1;i<=e;i++){
        y[i] = a[i];
    }
    mergeSort(x,s,mid);
    mergeSort(y,mid+1,e);
    mergeArrays(x,y,a,s,e);
}

int main(){
  int a[] = {7,3,10,5,6,2,-5};
  mergeSort(a,0,6);

  for(int i=0;i<7;i++){
    cout<<a[i]<<" ";
  }
  return 0;
}





Below solution is better
Always use below solution


void merge(int *a,int s,int e){
    int mid = (s+e)/2;
    
    int i = s;
    int j = mid+1;
    int k = s;
    
    int temp[100];
    
    while(i<=mid && j<=e){
        if(a[i] < a[j]){
            temp[k++] = a[i++];
        }
        else{
            temp[k++] = a[j++];
        }
    }
    while(i<=mid){
        temp[k++] = a[i++];
    }
    while(j<=e){
        temp[k++]  = a[j++];
    }
    
    //We need to copy all element to original arrays
    for(int i=s;i<=e;i++){
        a[i] = temp[i];
    }
    
    
}

void mergeSort(int a[],int s,int e){
    //Base case - 1 or 0 elements
    if(s>=e){
        return;
    }
    
    //Follow 3 steps
    //1. Divide
    int mid = (s+e)/2;
    
    //Recursively the arrays - s,mid and mid+1,e
    mergeSort(a,s,mid);
    mergeSort(a,mid+1,e);
    
    //Merge the two parts
    merge(a,s,e);

}