The smart-ass answer:
int old; std::cin >> old;
The horrible answer:
int old, dummy = (std::cin >> old, 0);
The proper answer: old
has to be defined with a declaration before it can be passed to operator>>
as an argument. The only way to get a function call within the declaration of a variable is to place it in the initialization expression as above. The accepted way to declare a variable and read input into it is as you have written:
int old;
std::cin >> old;