why the output are not the same?

Question

I checked both by compiler that:

The output of this is 10

    int count = 0; 
    for(int i=0; i < 10; ++i){ 
            count=++count;
    }
    cout << count; 

I don't get why the output of this(++count becomes count++) is 0

    int count = 0; 
    for(int i=0; i < 10; ++i){ 
            count=count++;
    }
    cout << count; 

Answer 1

With

        count=++count;

and

        count=count++;

both programs run into undefined behaviour as you are modifying count without an intervening sequence point. Note that = operator doesn't introduce a sequence point.

Obligatory read on UB ;-)

Undefined Behavior and Sequence Points in C++