merge sort

#include <iostream>
using namespace std;
void merge(int a[],int lb,int mid,int ub)
{
    int b[ub+1];
    int i=lb;
    int j=mid+1;
    int k=lb;
    while(i<=mid && j<=ub)
    {
        if(a[i]<a[j])
        {
            b[k]=a[i];
            i++;
        }
        else if(a[j]<a[i])
        {
            b[k]=a[j];
            j++;
        }
        k++;
    }
    if(i>mid)
    {
        while(j<=ub)
        {
            b[k]=a[j];
            i++;j++;
        }
    }
    else if(j>ub)
    {
        while(i<=mid)
        {
            b[k]=a[i];
            i++;k++;
        }
    }
    for(int k=0;k<=ub;k++)
    {
        a[i]=b[k];
    }
    
}
void mergesort(int a[],int lb,int ub)
{
    if(lb<ub)
    {
    int mid=(lb+ub)/2;
    mergesort( a,lb, mid);
    mergesort( a, mid+1,ub);
    merge( a,lb,mid, ub);
    }
}

int main()
{
    int a[100];
    int n;
    cout<<"Enter the no. of element";
    cin>>n;
    cout<<"Enter the element";
    for(int i=0;i<n;i++)
    {
        cin>>a[i];
    }
    int b[100];
    int ub=n-1;
    int lb=0;
    mergesort(a,lb,ub);
    cout<<"Array after sorting"<<endl;
    for(int i=0;i<n;i++)
    {
        cout<<a[i];
        cout<<" ";
        
    }
    
    
}