Infinite Loop

Question

Why when changing x++; to x=x++; cause an infinite loop?

while (x<=20)
{
cout<<x<<endl;
x=x++;
}

Answer 1

It's not strange at all, since the value of x remains 0. If you understand how post increment works, it becomes very easy to see why. The behaviour of x++ is to increase x by 1 and return the old value of x. The steps involved in x=x++ are:
1. the right hand side (x++) returns x
2. increments x by 1
3. assigns x to old value of x, returned in step 1
hence x does not change.
x=x++ is equivalent to
int oldValue = x;
x++;
x=oldValue;

to get your intended you should just use x++ or ++x or x=++x (the last code redunant though)