lambda.cpp

// lambda.cpp ---- 使用 lambda 表达式

#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <ctime>

const long Size1 = 39L;
const long Size2 = 100 * Size1;
const long Size3 = 100 * Size2;
bool f3(int x) {return x % 3 == 0;}
bool f13(int x) {return x % 13 == 0;}

int main()
{
    using std::cout;
    std::vector<int> numbers(Size1);

    std::srand(std::time(0));
    std::generate(numbers.begin(), numbers.end(),std::rand);

    // using function pointers
    court << "Sample size = " << Size1 << '\n';

    int count3 = std::count_if(numbers.begin(),numbers.end(),f3);
    cout << "Count of nuumbers divisible by 3 : " << count3 << '\n';
    int count13 = std::count_if(numbers.begin(),numbers.end(),f13);
    cout << "Count of numbers divisible by 13 : " << count13 << "\n\n";

    // increase number of numbers
    numbers.resize(Size2);
    std::generate(number.begin(),number.end(),std::rand);
    cout << "Sample size = " << Size2 << '\n';

    // using a functor
    class f_mod
    {
        private:
            int dv;
        public:
            f_mod(int d = 1) : dv(d) {}
            bool operator() (int x) {return x % dv == 0;}
    };

    count3 = std::count_if(numbers.begin().numbers.end(),f_mod(3));
    cout << "Count of numbers divisible by 3 : " << count3 << '\n';
    count13 = std::count_if(numbers.begin(),numbers.end(),f_mod(13));

    // increase number of numbers again
    numbers.resize(Size3);
    std::generate(numbers.begin(),numbers.end(),std::rand);
    cout << "Sample size = " << Size3 << '\n';

    // using lambdas

    count3 = std::count_if(numbers.begin(),numbers.end(),[](int x) {return x % 3 == 0;});
    cout << "Count of numbers divisible by 3 : " << count3 << '\n';
    count13 = std::count_if(numbers.begin(),numbers.end(), [] (int x){return x % 13 == 0;});
    cout << "Count of numbers divisible by 13 : " << count13 << '\n';

    return 0;
}