Calculate Fibonacci number in C++
problem
You would like to calculate the nth Fibonacci number using the C++ programming language. Recall that the sequence of Fibonacci as follows:
SOLUTION
Let’s use recursion as the mathematical problem has a recursive nature. The function prototype will look as follow:
long int fibonacci(int fth);
The implementation of it will be as follows:
long int fibonacci(int fth) {
if (fth == 0) {
return 0;
}else if (fth == 1){
return 1;
}else {
return fibonacci(fth-1) + fibonacci(fth-2);
}
}
We assume that the input will always be positive otherwise it will result in stack overflow error.
Putting it all together with a main method that will call fibonacci with an argument of 10 and print the result:
#include <iostream>
using namespace std;
long int fibonacci(int fth);
int main() {
cout << fibonacci(10) << endl;
return 0;
}
long int fibonacci(int fth) {
if (fth == 0) {
return 0;
}else if (fth == 1){
return 1;
}else {
return fibonacci(fth-1) + fibonacci(fth-2);
}
}
compiling
In terminal, I used g++ for compiling as follows:
g++ fibo.cpp
By default the output file is a.out (on Mac or Linux)
running
./a.out
output
Prints 55 on the screen which is correct!
The 10th Fibonacci (F10) in the sequence is 55 as shown below (starting from 1):
1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233 …
conclusion
In this post we saw how to calculate the nth number in the Fibonacci sequence using recursion. Please feel free to check out more of C++ coding tutorials