Question

Add comments on this Fibonacci C++ program in detail.

#include <iostream>
using namespace std;

int fib(int n){
   int a = 0,b = 1,c;
   if(n == 0 || n == 1){
      return n;
   }
   while(n>2){
      c = b + a;
      a = b;
      b = c;
      n--;
   }
   return c;
}

int main(){
   int n;
   cout<<"Enter n: ";
   cin>>n;
   int result = fib(n);
   cout<<"Fib("<<n<<") = "<<result<<endl;
   return 0;
}

Answer 1

#include <iostream>

using namespace std;

int fib(int n) {
    int a = 0, b = 1, c;
    if (n == 0 || n == 1) { // if n is 0 or 1, then return n. because fibonacci of 0 is 0 and fibonacci of 1 is 1
        return n;
    }
    while (n > 2) { // as long as n is greater than 2
        // a and b are fibonacci numbers
        // set a to b
        // and set b to sum of previous two terms
        c = b + a;  // calculate fibonacci of next number. fibonacci of n is sum of previous two fibonacci numbers
        a = b;  // set a to b
        b = c;  // set b to sum of previous two terms which is stored in c
        n--;    // decrement value of n
    }
    return c;   // return the calculated fibonacci number 
}

int main() {
    int n;
    cout << "Enter n: ";    // ask user to enter a number
    cin >> n;   // read a number
    int result = fib(n);    // determine fibonacci of n 
    cout << "Fib(" << n << ") = " << result << endl;    // print fibonacci of n to screen
    return 0;
}