Coin Sum Problem All Combination Program in C C++

#include<bits/stdc++.h>
using namespace std;

int calc(int ar[],int m,int n)
{
if(n==0)
return 1;
if(n<0)
return 0;
if(m<=0 &&n>=1)
return 0;

return calc(ar,m-1,n)+calc(ar,m,n-ar[m-1]);
}
main()
{
int ar[]={1,2,3};
int size=3;
int sum=4;
int count;
count=calc(ar,size,sum);
cout<<count;
}