87 lines
3.6 KiB
C++
87 lines
3.6 KiB
C++
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// fig15_19.cpp
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// Calculating factorials at compile time.
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#include <iostream>
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// Factorial value metafunction calculates factorials recursively
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template <int N>
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struct Factorial {
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static constexpr long long value{N * Factorial<N - 1>::value};
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};
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// Factorial specialization for the base case
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template <>
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struct Factorial<0> {
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static constexpr long long value{1}; // 0! is 1
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};
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// constexpr compile-time recursive factorial
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constexpr long long recursiveFactorial(int number) {
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if (number <= 1) {
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return 1; // base cases: 0! = 1 and 1! = 1
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}
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else { // recursion step
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return number * recursiveFactorial(number - 1);
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}
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}
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// constexpr compile-time iterative factorial
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constexpr long long iterativeFactorial(int number) {
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long long factorial{1}; // result for 0! and 1!
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for (long long i{2}; i <= number; ++i) {
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factorial *= i;
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}
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return factorial;
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}
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int main() {
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// "calling" a value metafunction requires instantiating
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// the template and accessing its static value member
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std::cout << "CALCULATING FACTORIALS AT COMPILE TIME "
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<< "WITH A RECURSIVE METAFUNCTION"
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<< "\nFactorial(0): " << Factorial<0>::value
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<< "\nFactorial(1): " << Factorial<1>::value
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<< "\nFactorial(2): " << Factorial<2>::value
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<< "\nFactorial(3): " << Factorial<3>::value
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<< "\nFactorial(4): " << Factorial<4>::value
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<< "\nFactorial(5): " << Factorial<5>::value;
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// calling the recursive constexpr function recursiveFactorial
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std::cout << "\n\nCALCULATING FACTORIALS AT COMPILE TIME "
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<< "WITH A RECURSIVE CONSTEXPR FUNCTION"
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<< "\nrecursiveFactorial(0): " << recursiveFactorial(0)
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<< "\nrecursiveFactorial(1): " << recursiveFactorial(1)
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<< "\nrecursiveFactorial(2): " << recursiveFactorial(2)
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<< "\nrecursiveFactorial(3): " << recursiveFactorial(3)
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<< "\nrecursiveFactorial(4): " << recursiveFactorial(4)
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<< "\nrecursiveFactorial(5): " << recursiveFactorial(5);
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// calling the iterative constexpr function iterativeFactorial
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std::cout << "\n\nCALCULATING FACTORIALS AT COMPILE TIME "
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<< "WITH AN ITERATIVE CONSTEXPR FUNCTION"
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<< "\niterativeFactorial(0): " << iterativeFactorial(0)
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<< "\niterativeFactorial(1): " << iterativeFactorial(1)
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<< "\niterativeFactorial(2): " << iterativeFactorial(2)
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<< "\niterativeFactorial(3): " << iterativeFactorial(3)
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<< "\niterativeFactorial(4): " << iterativeFactorial(4)
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<< "\niterativeFactorial(5): " << iterativeFactorial(5) << "\n";
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}
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/**************************************************************************
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* (C) Copyright 1992-2022 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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