Question

Use the functions below to write a C++ program to find the smallest Fibonacci number greater than 1,000,000 and greater than 1,000,000,000.

#include <iostream>
using namespace std;

int fibonacci(int n) {
int a = 0, b = 1, c;
if (n <= 1)
return n;
for (int i = 2; i <= n; i++) {
c = a + b;
a = b;
b = c;
}
return b;
}

int fibonacciRecursive(int n) {
if (n <= 1) {
return n;
}
return fibonacciRecursive(n-1) + fibonacciRecursive(n-2);
}

int main() {
int n;
cout << "Enter a value for n: ";
cin >> n;
cout << n << "th fibonacci number is " << fibonacci(n) << endl;
cout << n << "th fibonacci number is " << fibonacciRecursive(n) << endl;
return 0;
}

Answer 1

#include <iostream>
using namespace std;

int fibonacci(int n) {
long int a = 0, b = 1, c;
if (n <= 1)
return n;
for (int i = 2; i <= n; i++) {
c = a + b;
a = b;
b = c;
// if b cross 1000000 then return
if(b>n)
return b;
}
return b;
}

int main() {
long int n=1000000;//just limit for fibonacci series

cout <<" fibonacci number Greator than 1000000 is " << fibonacci(n) << endl;
n=1000000000;
cout <<" fibonacci number Greator than 1000000000 is " << fibonacci(n) << endl;

return 0;
}

/*

fibonacci number Greator than 1000000 is 1346269
fibonacci number Greator than 1000000000 is 1134903170

*/