Why are the results different?

Question

#include <iostream>
using namespace std;

int main() {
int i=3;
int b=4;
cout<< ++i + b++;
return 0;
}

Result is 8.

#include <iostream>
using namespace std;

int main() {
int i=3;
cout<< ++i + i++;
return 0;
}

Result is 9.

Why are the results different?

Answer 1

In the first case, i is incremented prior to statement evaluation, while b is incremented after statement evaluation. During evaluation, i is 4 and b is 4. Outputs 8.

As for the second case, it has a catch.
https://stackoverflow.com/questions/4176328/undefined-behavior-and-sequence-points

Answer 2

case 1:
i=3;
b=4;
cout ++i (prefix) mean it will increase 1 that mean 4;
b++(safix)that mean it will increase after , practical it will be in the same position b=4 in this situation

so the answer is 8;

second case:
i=3
++i mean (prefix) 1 increment
i++ mean (safix) remain at the same position in this situation.

so actually the answer in addition we get 7 not 9.