How does the sizeof operator works?

Question

Please explain why the output of below code is showing s=4 and x=10?
void main{
int x=10, s=0;
s=sizeof(x=x+20);
cout<<s<<" "<<x;
}

Answer 1

"x = x + 20" is an expression of type int, so it is 4 bytes. sizeof gets replaced by a constant at compile-time, so the code itself is never executed.