modern-cpp-tutorial/code/2/2.02.constexpr.cpp at master · githubbadguy/modern-cpp-tutorial

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// 2.2.constexpr.cpp

// chapter 2 language usability

// modern cpp tutorial

// created by changkun at changkun.de

// https://github.com/changkun/modern-cpp-tutorial

#include <iostream>

#define LEN 10

int len_foo() {

int i = 2;

return i;

}

constexpr int len_foo_constexpr() {

return 5;

}

// error in c++11

// constexpr int fibonacci(const int n) {

// if(n == 1) return 1;

// if(n == 2) return 1;

// return fibonacci(n-1) + fibonacci(n-2);

// }

// ok

constexpr int fibonacci(const int n) {

return n == 1 || n == 2 ? 1 : fibonacci(n-1) + fibonacci(n-2);

}

int main() {

char arr_1[10]; // legal

char arr_2[LEN]; // legal

int len = 10;

// char arr_3[len]; // illegal

const int len_2 = len + 1;

constexpr int len_2_constexpr = 1 + 2 + 3;

// char arr_4[len_2]; // illegal, but ok for most of the compilers

char arr_4[len_2_constexpr]; // legal

// char arr_5[len_foo()+5]; // illegal

char arr_6[len_foo_constexpr() + 1]; // legal

// 1, 1, 2, 3, 5, 8, 13, 21, 34, 55

std::cout << fibonacci(10) << std::endl;

return 0;

}