My Ansi C Fibonacci code stinks! obvious bug?

This is a discussion on My Ansi C Fibonacci code stinks! obvious bug? within the C Programming forums, part of the General Programming Boards category; I know I have an obvious bug -- well, a calculation error somewhere. Doing a quick fibonacci code sample, only ...

  1. #1
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    My Ansi C Fibonacci code stinks! obvious bug?

    I know I have an obvious bug -- well, a calculation error somewhere. Doing a quick fibonacci code sample, only requirements is NOT to use arrays and NOT to do it recursively.

    This is what I came up with, and its obviously wrong!

    Code:
    int fibonacci(int userinput)
    
    {
    
    int result = 0;
    int counter = 0;
    
    if (userinput == 0) return result = 0;
           else if (userinput == 1) return result = 1;
                 else		
                      for (counter = userinput; counter > 1; counter--)
                            {
                              result += ((counter - 1) + (counter - 2));
                            }
    return (result);
    }
    I am sure the "bad guy" is the line result += (...) but what is wrong?

  2. #2
    Registered User
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    This version actually works, but how can I improve it?
    Code:
    int fibonacci(int userinput)
    { 
    
                if (userinput < 2) 
                    return userinput; 
    
                else  
                { 
                    int n1 = 1, n2 = 1, tmp = 0; 
    
                    for (int i = 2; i < userinput; i++) 
                    { 
                        tmp = n2; 
                        n2 = n1 + n2; 
                        n1 = tmp; 
                    } 
    
                    return n2; 
                } 
            }

  3. #3
    CSharpener vart's Avatar
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    Quote Originally Posted by Hansie View Post
    This version actually works, but how can I improve it?
    Code:
    int fibonacci(int userinput)
    { 
    
                if (userinput < 2) 
                    return userinput; 
    
                else  
                { 
                    int n1 = 1, n2 = 1, tmp = 0; 
    
                    for (int i = 2; i < userinput; i++) 
                    { 
                        tmp = n2; 
                        n2 = n1 + n2; 
                        n1 = tmp; 
                    } 
    
                    return n2; 
                } 
            }

    you can name your vars in more readable way and add comments explaining what is going on for one who does not know the algorithm...
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  4. #4
    Math wizard
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    Fibonacci sequence - isn't that the sequence 1, 1, 2, 3, 5, 8, 13, 21, etc.? If so, then what you need are two numbers that form the starting point. For the next number, you add the previous 2 numbers. It continues like that. Study the pattern and write the program for it that follows the pattern. I can see that you apparently have this in your code, but comments and better variable names would be helpful. The output could be named "output", the previous number as "PrevNumber" and the one before it "Prev2Number" (use whatever, but something more clear than "n1" and "n2").
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  5. #5
    Woof, woof! zacs7's Avatar
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    You should refer to the first 3 'elements' of the Fibonacci sequence as 'a', 'b' & 'c'. Since that makes sense, c = a + b, where a = 1 (first iteration) and b = 2 (first iteration).

    Then on the Nth iteration, a = b, b = c, c = a+b

    Such as, 1 (a), 2 (a,b), 3(a,b,c), 5 (a,b,c), 8 (a,b,c), etc

    And there is a mathematical way to get the Nth element of the Fibonacci sequence using a formula, rather than using a bruteforce method.
    Last edited by zacs7; 05-23-2007 at 01:35 AM.

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