Pseudocode to actual code of linear fibonacci - c++

Question

We are trying to convert this pseudocode into an actual code. The pseudo code is
Algorithm LinearFibonacci(k):
Input: A nonnegative integer k
Output: Pair of Fibonacci numbers (Fk,Fk−1)
if k ≤ 1 then
return (k,0)
else
(i, j)← LinearFibonacci(k−1)
return (i+ j, i)
I tried to translate it and came up with this
pair<int,int> LinearFibonnaci(int k) {
int i = 0;
int j = 0;
if (k <= 1) {
return make_pair(k, 0);
}
else {
make_pair(i, j) = LinearFibonnaci(k - 1);
return make_pair(i + j, i);
}
}
Am i doing this corretly because im not sure how to print out a pair function?

Answer 1

A std::pair object (not function) has two public members, first and second.
Since C++11, you can also extract an element from a pair using std::get.
See the following examples (testable here):
#include <iostream>
#include <utility>
#include <tuple>
std::pair<int, int> LinearFibonnaci(int k);
int main()
{
int k = 3;
// Explicitly declaring the type
std::pair<int, int> f = LinearFibonnaci(k);
// ^^^^^^^^^^^^^^^^^^^
std::cout << "F(" << k << ") = "
<< f.first << ", F(" << (k - 1) << ") = " << f.second << '\n';
// ^^^^^^^ ^^^^^^^^
k = 4;
// Since C++11: Using 'auto' let the compiler deduce the type
auto g = LinearFibonnaci(k);
// ^^^^
std::cout << "F(" << k << ") = "
<< g.first << ", F(" << (k - 1) << ") = " << g.second << '\n';
// ^^^^^^^ ^^^^^^^^
k = 5;
// Since C++17: Structured binding declaration
// See e.g. https://en.cppreference.com/w/cpp/language/structured_binding
auto [n, m] = LinearFibonnaci(k);
// ^^^^^^^^^^^
std::cout << "F(" << k << ") = " << n << ", F(" << (k - 1) << ") = " << m << '\n';
// ^^^ ^^^
k = 8;
// Since C++11: std::tie
// See e.g. https://en.cppreference.com/w/cpp/utility/tuple/tie
std::tie(n, m) = LinearFibonnaci(k);
// ^^^^^^^^^^^^^^
std::cout << "F(" << k << ") = " << n << ", F(" << (k - 1) << ") = " << m << '\n';
// ^^^ ^^^
k = 12;
// Since C++11: std::get
// https://en.cppreference.com/w/cpp/utility/pair/get
auto h = LinearFibonnaci(k);
std::cout << "F(" << k << ") = " << std::get<0>(h)
// ^^^^^^^^^^^^^^
<< ", F(" << (k - 1) << ") = " << std::get<1>(h) << '\n';
// ^^^^^^^^^^^^^^
}
std::pair<int, int> LinearFibonnaci(int k)
{
int i = 0;
int j = 0;
if (k <= 1) {
return {k, 0}; // You can use the constructor, here
}
else {
std::tie(i, j) = LinearFibonnaci(k - 1);
return {i + j, i};
}
}

Answer 2

As this question is marked C++17, structured bindings (auto[i,j]) can be used.
Another thing is that by using curly braces we can directly initialize the std::pair return object.
std::pair<int,int> LinearFibonnaci(int k) {
if (k <= 1)
{
return {k, 0};
}
else
{
auto[i, j] = LinearFibonnaci(k - 1);
return {i + j, i};
}
}
To get the result, again structured bindings can be used to retrieve the values:
auto[i, j] = LinearFibonnaci(x);