int main() {
    int i=1;
    i=++i + i++;
    std::cout<<i<<std::endl;
    return 0;
}

here the output is 5

int main() { 
    int i=1;
    i=i++ + i++ + i++;
    std::cout<<i<<std::endl;
    return 0;
}

here the output is 6

in the first code if we ignore the last increment we get 4 which is wrong but in the second code if we ignore the last increment we get 6 which is right.

both codes have post increment at the end of the equation