### generate number

New target:

I would like to generate number from sumerizing of the previous numbers like this:

 ``12`` ``````// 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 // 2 4 7 11 16 23 30 38 47 57 68 80 93 107 122 138 150 168 ``````

Can you help what do I need change?

http://www.cplusplus.com/forum/beginner/3212/

code of pet:
 ``1234567891011121314151617181920212223242526`` ``````#include #include using namespace std; int fib(int n) { if(1 == n || 2 == n) { return 1; } else { return fib(n-1) + fib(n-2); } } int main() { for(int i=1; i<=15; i++) { cout << fib(i) << endl; } getch(); return 0; }``````

Is it posible to make function to this one, having ability to get the number i, when you know the Fibonacci number?
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You mean a function with output like this?

 ``` Please input Fibonacci number: 8 8 is 6. Fibonacci number ```

It certainly is possible, but you will have to create a new function :)
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Perhaps this might help - there's mountains of information on the Fibonacci numbers here, and your specific question is discussed, with a formula given, as well as an online demonstration.
http://www.maths.surrey.ac.uk/hosted-sites/R.Knott/Fibonacci/fibFormula.html#detectfib
MatthewRock
I mean, when FN is 610, what is n? n is 15.
When I know that n is 15, so I can generate new FN: either lower or greater:
fib(15-1);fib(15+1); depending on what I need.
Topic changed:

I would like to generate number from sumerizing of the previous numbers like this:

 ``1234567891011121314151617181920212223`` ``````#include #include using namespace std; // 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 // 2 4 7 11 16 23 30 38 47 57 68 80 93 107 122 138 150 168 int sum(int i, int &r) { r = i+r; return r; } int main() { int result=-1; int &r = result; for(int i=1; i<=30; i++) { cout << i << " : " << sum(i, r) << endl; } _getch(); return 0; } ``````

I tried to initiate the number result as 0 (higher numbers) or -1 a smaller numbers (not ideal because at i=1 should be r=1 or higher. Any idea how to correct this to give this?
2 4 7 11 16 23 30 38 47 57 68 80 93 107 122 138 150 168
I tried to simplify as much as possible
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