Not getting right output for largest subarray with sum k

#1

#include
#include<unordered_map>
using namespace std;

int checksum(int arr[],int n,int k)
{
unordered_map<int,int> mp;
int pre=0;
int len=0;
for(int i=0;i<n;i++)
{
pre+=arr[i];

	if(pre==k)
    len=max(len,i+1);
	if(mp.find(pre-k)!=mp.end())
	{
		len=max(len,i-mp[pre-k]);
	}
	else
	{
		mp[pre]=i;
	}
}
return len;

}
int main()
{
int n;
cin>>n;
int arr[n];

for(int i=0;i<n;i++)
{
	cin>>arr[n];
}
int k;
cin>>k;
int b=checksum(arr,n,k);
cout<<b;

}