90 lines
3.4 KiB
C++
90 lines
3.4 KiB
C++
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// fig14_18.cpp
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// Working with C++20 std::views.
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#include <algorithm>
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#include <iostream>
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#include <iterator>
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#include <map>
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#include <ranges>
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#include <string>
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#include <vector>
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int main() {
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std::ostream_iterator<int> output{std::cout, " "};
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auto isEven{[](int x) {return x % 2 == 0;}}; // true if x is even
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// infinite view of even integers starting at 0
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auto evens{std::views::iota(0) | std::views::filter(isEven)};
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std::cout << "First five even ints: ";
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std::ranges::copy(evens | std::views::take(5), output);
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std::cout << "\nEven ints less than 12: ";
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auto lessThan12{
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evens | std::views::take_while([](int x) {return x < 12;})};
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std::ranges::copy(lessThan12, output);
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std::cout << "\nEven ints less than 12 reversed: ";
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std::ranges::copy(lessThan12 | std::views::reverse, output);
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std::cout << "\nSquares of even ints less than 12 reversed: ";
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std::ranges::copy(
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lessThan12
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| std::views::reverse
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| std::views::transform([](int x) {return x * x;}),
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output);
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std::cout << "\nSkip 1000 even ints, then take five: ";
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std::ranges::copy(
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evens | std::views::drop(1000) | std::views::take(5),
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output);
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std::cout << "\nFirst five even ints greater than 1000: ";
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std::ranges::copy(
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evens
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| std::views::drop_while([](int x) {return x <= 1000;})
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| std::views::take(5),
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output);
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// allow std::string object literals
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using namespace std::string_literals;
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std::map<std::string, int> romanNumerals{
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{"I"s, 1}, {"II"s, 2}, {"III"s, 3}, {"IV"s, 4}, {"V"s, 5}};
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auto displayPair{[](const auto& p) {
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std::cout << p.first << " = " << p.second << "\n"; }};
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std::cout << "\n\nromanNumerals:\n";
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std::ranges::for_each(romanNumerals, displayPair);
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std::ostream_iterator<std::string> stringOutput{std::cout, " "};
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std::cout << "\nKeys in romanNumerals: ";
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std::ranges::copy(romanNumerals | std::views::keys, stringOutput);
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std::cout << "\nValues in romanNumerals: ";
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std::ranges::copy(romanNumerals | std::views::values, output);
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std::cout << "\nKeys in romanNumerals via std::views::elements: ";
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std::ranges::copy(
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romanNumerals | std::views::elements<0>, stringOutput);
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std::cout << "\nvalues in romanNumerals via std::views::elements: ";
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std::ranges::copy(romanNumerals | std::views::elements<1>, output);
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std::cout << "\n";
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}
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/**************************************************************************
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* (C) Copyright 1992-2021 by Deitel & Associates, Inc. and *
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* Pearson Education, Inc. All Rights Reserved. *
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* *
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* DISCLAIMER: The authors and publisher of this book have used their *
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* best efforts in preparing the book. These efforts include the *
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* development, research, and testing of the theories and programs *
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* to determine their effectiveness. The authors and publisher make *
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* no warranty of any kind, expressed or implied, with regard to these *
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* programs or to the documentation contained in these books. The authors *
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* and publisher shall not be liable in any event for incidental or *
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* consequential damages in connection with, or arising out of, the *
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* furnishing, performance, or use of these programs. *
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**************************************************************************/
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