# Generating large Fibonacci numbers using boost library

In our previous post on fibonacci series, we have seen many approaches to generate fibonacci numbers. In this approach, we shall be generating fibonacci numbers with the help of boost library. The program simply uses the “boost/multiprecision/cpp_int.hpp” boost library in which big_int is defined. The fibonacci numbers beyond the range of long long int can also be generated using the boost library. Below is the C++ implementation to generate fibonacci numbers using the boost library.

 `// C++ implementation to generate large ` `// number of fibonacci series using the  ` `// boost multiprecision library ` `#include ` `#include ` `using` `big_int = boost::multiprecision::cpp_int; ` `using` `namespace` `std; ` ` `  `// function to generate first n ` `// fibonacci numbers ` `int` `fib(unsigned ``int` `n) ` `{ ` `    ``// seed values ` `    ``// 0th and 1st number of the ` `    ``// series are 0 and 1 ` `    ``big_int a = 0; ` `    ``big_int b = 1; ` `    ``cout << ``"Term 1 is : "` `<< a << endl;  ` `    ``cout << ``"Term 2 is : "` `<< b << endl; ` `     `  `    ``for` `(unsigned ``int` `i = 2; i < n; ++i) ` `    ``{ ` `        ``const` `big_int c = a + b; ` `        ``cout << ``"Term "``<< i + 1 << ``" is : "` `<< c << endl; ` `        ``a = b; ` `        ``b = c; ` `    ``} ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``unsigned ``int` `n = 30; ` `     `  `    ``// function calling ` `    ``fib(n); ` `     `  `    ``return` `0; ` `} `

Output :

```Term 1 is : 0
Term 2 is : 1
Term 3 is : 1
Term 4 is : 2
Term 5 is : 3
Term 6 is : 5
Term 7 is : 8
Term 8 is : 13
Term 9 is : 21
Term 10 is : 34
Term 11 is : 55
Term 12 is : 89
Term 13 is : 144
Term 14 is : 233
Term 15 is : 377
Term 16 is : 610
Term 17 is : 987
Term 18 is : 1597
Term 19 is : 2584
Term 20 is : 4181
Term 21 is : 6765
Term 22 is : 10946
Term 23 is : 17711
Term 24 is : 28657
Term 25 is : 46368
Term 26 is : 75025
Term 27 is : 121393
Term 28 is : 196418
Term 29 is : 317811
Term 30 is : 514229
```
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