why does this output 5? confused

Question

int sum(int *p, int size)
{
int sum=0;
for(int i=0; i<size; i++)
{
sum+=p[i];
}
return sum;
}

int main()
{
int arr[4]={1,2,3,4};

int result=sum(&arr[1],2);///passing in address of arr[1] and passing in 2 to size
cout<<result;
}

Answer 1

arr = {1,2,3,4}
&arr[1] = {2,3,4}
you pass 2 to the function size, so only takes 2+3, it's 5

Answer 2

By passing the address of arr[i] you pass to the sum function the address of the array that starts at index i of arr (the array {2, 3, 4}). In other words:

int arr[4] = {1, 2, 3, 4);
int arr2[3] = {2, 3, 4};

int result = sum (&arr[1], 2);
int result1 = sum (arr + 1, 2);
int result2 = sum (&arr2[0], 2);
int result3 = sum (arr2, 2);
All the above "results" are the same thing;

This happens because arr is the same thing as &arr[0] and arr + i is the same thing as &arr[i].

Hope this helped you!