can somebody tells me why this results in 6?

Question

int arr[3]={5,3,1};
int sum=0;
for (int i=0; i<3; i+=2){
sum+=arr[i];
}
cout<<sum;
/* I can't figure out the logic here. In the end of the for loop we get the value of i or in the beggining? I am lost in the relation between sum and for loop. Please for any explanation.*/

Answer 1

it does arr[0]+arr[2]

Answer 2

for loop runs for i=0 and i=2
So, sum =0 + 5; //5 for i = 0
sum= 5 +1; //6 for i = 2

Answer 3

sum=sum+arr[0]
sum=0+5
then
sum=5+arr[2]
sum=5+1

Answer 4

to do sum all array make
for(int i=0;i<3;i++)
{
sum+=arr[i];
}
now sum =9