Max Min Problem

This is a discussion on Max Min Problem within the C Programming forums, part of the General Programming Boards category; So here I am writing this code and I am having problems with something basic, but I think I am ...

  1. #1
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    Max Min Problem

    So here I am writing this code and I am having problems with something basic, but I think I am overlooking something simple. I am trying to read from a text file and compute mean, root mean, and Max height (which is the highest number - lowest number) It's coming up with some huge number so yea, I need a second opinion please! Here is the data file

    Code:
    -4.1 -2.2 -0.5  1.2  3.3  4.6  5.1  2.1  0.2 -3.6 -4.1  0.2
     0.5  2.2  4.1 -0.2 -1.2 -3.3 -4.6 -5.0 -2.2 -1.1  0.8	3.2
    -0.1 -4.8
    And here is the Code

    Code:
    /* Christopher R Smith
    COMP1200 - Fall 2008
    Assignment 6
    Program: Average Value Program
    
    -------------------------------------------------------------------------------------------------------------
    Taking surface measurements from a text file, compute and display the Arithmetic Mean Value, the
    Root Mean Square Average, and the Max Roughness Height
    
    --------------------------------------------------------------------------------------------------------------
    */
    
    #include <stdio.h>
    #include <math.h>
    
    int main()
    {
    FILE 		*inp;
    double	value, 	
    			mean,
    			root_mean_square,
    			sum=0,
    			max_height;
    int 		numValue=0,
    			count;
    		
    
    inp = fopen("surface.txt", "r");		
    
    while ( ( fscanf ( inp,"%lf", &value ) ) == 1 )
    	{
    		  sum += fabs(value);
    		  numValue++;
    		  
    	}
    
    mean = sum / numValue;
    
    while ( ( fscanf ( inp,"%lf", &value ) ) == 1 )
    	{
    		  sum += pow( fabs(value), 2 );
    		  numValue++;
    		  
    	}
    
    root_mean_square = sqrt( sum / numValue);
    
    
    
    while ( ( fscanf ( inp,"%lf", &value ) ) == 1 )
    	{
    		double max=-10000, min=10000;
    
    				
    				if (value >= max)
    						max = value;
    				else 
    						min = value;
    							
    		;
    			max_height = max - min
    	}
    		
    
    	
    printf( "Arithmetic mean value %.2lf\n", mean);
    printf( "Root-mean-square average %.2lf\n", root_mean_square);
    printf( "Maximum roughness height %.2lf\n", max_height);					
    
    
    
    
    
    
    
    return (0);
    }
    This problem is probably coming from this segment of code

    Code:
    while ( ( fscanf ( inp,"%lf", &value ) ) == 1 )
    	{
    		double max=-10000, min=10000;
    
    				
    				if (value >= max)
    						max = value;
    				else 
    						min = value;
    							
    		;
    			max_height = max - min
    	}
    I am receiving this output

    Code:
    Arithmetic mean value 2.48
    Root-mean-square average 1.58
    Maximum roughness height 1889828851749420549890302903237191694835027000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.00
    Is that huge number some other value somewhere else in the computer

  2. #2
    Chi! whiteflags's Avatar
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    First, calculate max_height after you run through the loop. And, remove the initialization from the loop body. Lastly, max and min need to be updated separately. I find this to be a eloquent solution:

    Code:
    double MAX ( double a, double b ) 
    {
      return a > b ? a : b;
    }
    
    double MIN ( double a, double b )
    {
      return a < b ? a : b;
    }
    
    /** call MAX and MIN like so **/
    
    double value;
    double max = -1000.0;
    double min = 1000.0;
    double max_height = 0.0;
    
    while ( 1 == fscanf( inp, "&#37;lf", &value ) ) {
      min = MIN( value, min );
      max = MAX( value, max );
    }
    
    max_height = max - min;
    Not yet compiled, but good enough ...
    Last edited by whiteflags; 10-22-2008 at 10:28 AM.

  3. #3
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    what if we aren't supposed to "know" how to make a user defined function like you did in

    Code:
    double MAX ( double a, double b )
    and

    Code:
    double MIN ( double a, double b )

  4. #4
    C++ Witch laserlight's Avatar
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    Then you just write what's in the loop body in the main function instead.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  5. #5
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    I am not sure if understand this part of the code

    Code:
    double MAX ( double a, double b ) 
    {
      return a > b ? a : b;
    }
    
    double MIN ( double a, double b )
    {
      return a < b ? a : b;
    }

    the

    Code:
    ? a : b;

  6. #6
    Chi! whiteflags's Avatar
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    That's the ternary operator: It's shorthand for an if-else. Feel free to ignore that and use an actual if-else in your code.

  7. #7
    and the hat of sweating
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    Quote Originally Posted by citizen View Post
    First, calculate max_height after you run through the loop. And, remove the initialization from the loop body. Lastly, max and min need to be updated separately. I find this to be a eloquent solution:

    Code:
    double MAX ( double a, double b ) 
    {
      return a > b ? a : b;
    }
    
    double MIN ( double a, double b )
    {
      return a < b ? a : b;
    }
    
    /** call MAX and MIN like so **/
    
    double value;
    double max = -1000.0;
    double min = 1000.0;
    double max_height = 0.0;
    
    while ( 1 == fscanf( inp, "%lf", &value ) ) {
      min = MIN( value, min );
      max = MAX( value, min );
    }
    
    max_height = max - min;
    Not yet compiled, but good enough ...
    What happens if you pass NaN to one of those functions?
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

    "the internet is a scary place to be thats why i dont use it much." - billet, 03/17/2010

  8. #8
    Chi! whiteflags's Avatar
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    >> What happens if you pass NaN to one of those functions?
    At a stab in the dark, I'm guessing it breaks, otherwise you wouldn't have mentioned it. But correct me wherever possible. And admittedly I did not consider NaNs while helping this lad with his assignment.

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