69 lines
2.9 KiB
C++
69 lines
2.9 KiB
C++
// fig06_13.cpp
|
|
// Functional-style programming with C++20 ranges and views.
|
|
#include <array>
|
|
#include <fmt/format.h>
|
|
#include <iostream>
|
|
#include <numeric>
|
|
#include <ranges>
|
|
|
|
int main() {
|
|
// lambda to display results of range operations
|
|
auto showValues{
|
|
[](auto& values, const std::string& message) {
|
|
std::cout << fmt::format("{}: ", message);
|
|
|
|
for (const auto& value : values) {
|
|
std::cout << fmt::format("{} ", value);
|
|
}
|
|
|
|
std::cout << '\n';
|
|
}
|
|
};
|
|
|
|
auto values1{std::views::iota(1, 11)}; // generate integers 1-10
|
|
showValues(values1, "Generate integers 1-10");
|
|
|
|
// filter each value in values1, keeping only the even integers
|
|
auto values2{values1 |
|
|
std::views::filter([](const auto& x) {return x % 2 == 0;})};
|
|
showValues(values2, "Filtering even integers");
|
|
|
|
// map each value in values2 to its square
|
|
auto values3{
|
|
values2 | std::views::transform([](const auto& x) {return x * x;})};
|
|
showValues(values3, "Mapping even integers to squares");
|
|
|
|
// combine filter and transform to get squares of the even integers
|
|
auto values4{
|
|
values1 | std::views::filter([](const auto& x) {return x % 2 == 0;})
|
|
| std::views::transform([](const auto& x) {return x * x; })};
|
|
showValues(values4, "Squares of even integers");
|
|
|
|
// total the squares of the even integers
|
|
std::cout << fmt::format("Sum squares of even integers 2-10: {}\n",
|
|
std::accumulate(std::begin(values4), std::end(values4), 0));
|
|
|
|
// process a container's elements
|
|
constexpr std::array numbers{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
|
|
auto values5{
|
|
numbers | std::views::filter([](const auto& x) {return x % 2 == 0;})
|
|
| std::views::transform([](const auto& x) {return x * x; })};
|
|
showValues(values5, "Squares of even integers in array numbers");
|
|
}
|
|
|
|
|
|
/**************************************************************************
|
|
* (C) Copyright 1992-2022 by Deitel & Associates, Inc. and *
|
|
* Pearson Education, Inc. All Rights Reserved. *
|
|
* *
|
|
* DISCLAIMER: The authors and publisher of this book have used their *
|
|
* best efforts in preparing the book. These efforts include the *
|
|
* development, research, and testing of the theories and programs *
|
|
* to determine their effectiveness. The authors and publisher make *
|
|
* no warranty of any kind, expressed or implied, with regard to these *
|
|
* programs or to the documentation contained in these books. The authors *
|
|
* and publisher shall not be liable in any event for incidental or *
|
|
* consequential damages in connection with, or arising out of, the *
|
|
* furnishing, performance, or use of these programs. *
|
|
**************************************************************************/
|