How C++ postfix incrementation works?

Question

Why output of below code is 5?

int b = 1;
b=++b+b++;
cout<<b;

and output of this code is 1?

int b = 1;
b=b++;
cout<<b;

Why in first example the b++ incrementation is added to result and in second case it is not? How does it work?

Answer 1

Just don't use multiple incrementations in the same line, it will only mess up the result!
What happens is that there are two increments, so b will be calculated to be 3 for the (++b) case and 2 for the (b++) case. 2+3 = 5 so the result is 5.
In the second example you calculate b++ first, but then set b to the old value of be, in this case 1.