What exactly is the difference between x++ and x+1?

Question

I've been thinking about this in terms of incrementing a pointer, but i guess in general now I don't know the semantic difference between these two operations/ operators. For example, my professor said that if you have int a[10] you can't say a++ to point at the next element, but I know from experience that a+1 does work. I asked why and he said something like "a++ is an action and a+1 is an expression". What did he mean by it's an "action"? If anyone could tell me more about this and the inherent difference between the two operations I'd greatly appreciate it. Thank you.

Answer 1

x++ and ++x

The increment operator x++ will modify and usually returns a copy of the old x. On a side note the prefixed ++x will still modify x but will returns the new x.

In fact x++ can be seen as a sort of:

{
    int temp = x; 
    x = x + 1; 
    return temp;
}

while ++x will be more like:

{
    x = x + 1;
    return x;
}

x + 1

The x+1 operation will just return the value of the expression and will not modify x. And it can be seen as:

{
    return (x + 1);
}