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Power Functions returning Zero

Discussion in 'Programming' started by Shae, Sep 30, 2007.

  1. Shae

    Shae New Member

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    Hey all,

    I think I must be brain damaged, because I am having the dumbest problem. I need a power function for a program, and every single one I use is returning zero at all times. I've tried the math.h pow() and two other functions, one recursive and one non-recursive.

    The frustrating thing is that this is a tiny, trivial part of what I'm trying to do (find the root of a scalar equation with newton's method), and I can't even seem to get out of the gate.

    I've tried compiling with g++ and gcc (need g++ for pow() of course), I've tried changing the value of j, swapping j and cx, changing the types of j and cx, and a whole bunch of other junk.

    Any help would be greatly appreciated.

    Here's the code, along with the debugging statements that prove to me that I'm getting the wrong answer.

    -------------------------------------------
    Code:
    #include<math.h>
    
    double calcPolyFunctionAtX(double cx);
    double power(double px, int y);
    double power2( double base, int exp );
    
    /* ********************* */
    
    /* Main */
    
    
    
    int main()
    
    {
    
    double f;
    
    /* unimportant stuff */
    
    f = calcPolyFunctionAtX(x); 
    
    /* unimportant stuff */
    }
    
    
    /* ********************* */
    /* Function for calculating polynomial at x */
    
    double calcPolyFunctionAtX(double cx){
    
    int j;
    double answer;
    answer = 0;
    double z;
    z = 0;
    
    	for(j=2; j<21; j++){
    
    		z = pow(cx, j);
    
    	printf("The value of cx is %d \n", cx); /* giving me correct values */
    	printf("The value of j is %i \n\n", j); /* giving me correct values */
    
            /* all of these are giving me incorrect values */
    	printf("The value of cx to the jth power by custom non-recursive power function is %d \n", power(cx, j) );
    printf("The value of j to the cxth power by custom non-recursive power function is %d \n", power(j, cx) );
    
    	printf("The value of cx to the jth power by built-in pow function is %d \n", pow(cx, j) );
    printf("The value of j to the cxth power by built-in pow function is %d \n", pow(j, cx) ); 
    
    	printf("The value of cx to the jth power by power2 recursive function is %d \n", power2(cx, j) );
    printf("The value of j to the cxth power by power2 recursive function is %d \n", power2(j, cx) ); */
    
    
    
    	}
    
    /* other junk */
    
    return answer;
    }
    
    double power(double px, int y){
    double product = 1.0;
    int g;
    
    for(g=1; g<=y; g++) {
    	product *= px;
    	}
    
    return product;
    
    }
    
    double power2( double base, int exp )
    {
    
    int i;
       if ( exp < 0 )
           return 1.0/power2(base, -exp);
    
      double product = 1.0;
    
      for ( i = 1 ; i <= exp ; i++ )
        product *= base;
    
      return product;
    }
     
    Last edited by a moderator: Oct 1, 2007
  2. An007kit

    An007kit New Member

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    The problem is that ya have used the specifier %d for double type......that is not valid.....i suggest try %l or %lf
     
  3. Shae

    Shae New Member

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    Thanks! I'll give that a try when I get off work. Although, I'm confused -- those functions all return a double, so shouldn't I specify a double?

    Thanks!
     
  4. DaWei

    DaWei New Member

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    %d is an integer....
     
  5. Shae

    Shae New Member

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    Ah, ok. Thanks DaWei. That might be causing me problems elsewhere too.
     
  6. Shae

    Shae New Member

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    Yeah.... so I used %f and now all the power functions are returning 0.000000.

    Any other ideas?

    Thanks in advance...
     
  7. Shae

    Shae New Member

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    Oh wait... my bad... it's working with %lf.

    Yay!!!

    Thanks to you both.
     

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