Differences between C# “var” and C++ “auto”

In C# var keyword works only locally inside function:

var i = 10; // implicitly typed 

In C++ auto keyword can deduce type not only in variables, but also in functions and templates:

auto i = 10;

auto foo() { //deduced to be int
    return 5;
}

template<typename T, typename U>
auto add(T t, U u) {
    return t + u;
}

From performance point of view, auto keyword in C++ does not affect runtime performance. And var keyword does not affect runtime performance as well.

Another difference can be in intellisense support in IDE. Var keyword in C# can be easily deduced and you will see the type with a mouse over. With auto keyword in C++ it might be more complicated, it depends on IDE and tooling.