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  1. #include <iostream>
  2.  
  3. using namespace std;
  4.  
  5. // compute fibonacci number for a given n>=0
  6.  
  7. int fibonacci(int n)
  8. {
  9.   int f, f1, f2;
  10.  
  11.   // for 0 and 1, just return the result right away
  12.  
  13.   if (n==0)
  14.     return 0;
  15.  
  16.   if (n==1)
  17.     return 1;
  18.  
  19.   // f1 and f2 store the previous two fibonacci numbers
  20.   // initialized to f1=0, and f2=1 (for fib0 and fib1).
  21.  
  22.   f1 = 0;
  23.   f2 = 1;
  24.  
  25.   // compute the next fibonacci number until we get
  26.   // to the target one
  27.  
  28.   for (int i=2; i<=n; i++)
  29.     {
  30.       // compute new fibonacci number
  31.       f = f1 + f2; 
  32.  
  33.       // move previous to one before the previous
  34.       // and move current into previous, for the next
  35.       // iteration (we are going to generate a new 
  36.       // number)
  37.  
  38.       f1 = f2;
  39.       f2 = f;
  40.     }
  41.  
  42.   return f;
  43. }
  44.  
  45. // main function
  46.  
  47. int main()
  48. {
  49.   int n;
  50.  
  51.   // read n from the user
  52.  
  53.   cin >> n;
  54.  
  55.   // compute and output the fibonacci number f(n)
  56.  
  57.   cout << "fib(" << n << ") = " << fibonacci(n) << endl;
  58.  
  59.   // return from main
  60.  
  61.   return 0;
  62. }
Success #stdin #stdout 0.02s 2684KB
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10
stdout
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Enter n:
fib(10) = 55
https://ideone.com/23FeL
language:
C++ (gcc 8.3)
created:
11 years ago
visibility:
secret

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