Exercise · Templates · lesson 11 of 11

Exercise: a running sum

Write the class template Tally, a running sum of values of type T; add the fields yourself. The variadic method template <typename... Ts> void add(Ts... xs) adds all its arguments to the sum. T total() const returns the sum, and int count() const returns how many values all calls to add received.

In the examples, points is a Tally<int>, grams a Tally<double>, and text a Tally<std::string>:

after points.add(3, 4, 5) and points.add(10): points.total() → 22, points.count() → 4
after grams.add(1.5, 2.25): grams.total() → 3.75
after text.add("ab", "cd") and text.add("ef"): text.total() → "abcdef"

Constraints: the arguments of add are numbers of type T or, for a Tally<std::string>, text in double quotes. Strings are joined in the order of the calls and the arguments, and calling add() with no arguments changes nothing.

sum_all.cpp — cpp

cpp · 16 lines

template <typename T>
class Tally {
public:
    template <typename... Ts>
    void add(Ts... xs) {
    }

    T total() const {
        return T{};
    }

    int count() const {
        return -1;
    }
};

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