Merge Sort in C++

#include <iostream>

using namespace std;
void merge(int*,int*,int,int,int);
void mergesort(int *a, int*b, int low, int high)

{
int pivot;
if(low<high)
{
pivot=(low+high)/2;
mergesort(a,b,low,pivot);
mergesort(a,b,pivot+1,high);
merge(a,b,low,pivot,high);
}
}
void merge(int *a, int *b, int low, int pivot, int high)
{
int h,i,j,k;
h=low;
i=low;
j=pivot+1;
while((h<=pivot)&&(j<=high))
{
if(a[h]<=a[j])
{
b[i]=a[h];
h++;
}
else
{
b[i]=a[j];
j++;
}
i++;
}
if(h>pivot)
{
for(k=j; k<=high; k++)
{
b[i]=a[k];
i++;
}
}
else
{
for(k=h; k<=pivot; k++)
{
b[i]=a[k];
i++;
}
}
for(k=low; k<=high; k++) a[k]=b[k];
}
int main()
{
int a[] = {12,10,43,23,-78,45,123,56,98,41,90,24};
int num;
num = sizeof(a)/sizeof(int);
int b[num];
mergesort(a,b,0,num-1);
for(int i=0; i<num; i++)
cout<<a[i]<<" ";
cout<<endl;
// system("pause");
}