can somebody please explain me this code

Question

#include<iostream>
using namespace std;
int add(int a[],int b)
{
int sum=0;
for(int i=0;i<b;i++){
sum+=a[i];
++a[i];

}
return sum;
}
int main(){
int arr[2][3]={{1,0,1},{1,2,3}};
int s=3;
cout<<"first "<<add(arr[0],s);
cout<<" second "<<add(arr[1],s);

}

Answer 1

It counts the sum of the sub array.

The function add has 2 params, a as array, b as array length to be counted.

Answer 2

1+0+1 = 2
1+2+3 = 6

Answer 3

Can you explain why it outputs 2 for first and 6 for second

Answer 4

I figured that out too but how does the code functions on the function call that is where i am stuck