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minmax

 
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  #1
Mar 30th, 2009
ok so im creating a program minmax to find the minimum and maximum numbers of an array. heres my code but i get segmentation fault where do you think im going wrong?

C Syntax (Toggle Plain Text) 
  1. #include <stdio.h>
  2. #include <stdlib.h>
  3.  
  4. void minmax( int numberlist[], int n, int *p_min, int *p_max );
  5.  
  6. int main( int argc, char *argv[] ){
  7.  
  8.   int *numberlist, i, n, *min, *max ;
  9.  
  10.   n = atoi( argv[1] );
  11.  
  12.   numberlist = ( int * ) malloc( n * sizeof( int ) );
  13.  
  14.   for( i = 0; i < n; i++ ) numberlist[i] == rand() % n ;
  15.  
  16.   minmax( numberlist, n, min, max );
  17.  
  18.   printf( "The minimum value in your array is: %d", *min );
  19.   printf( "The maximum value in your array is: %d", *max );
  20.  return 0;
  21. }
  22.  
  23. void minmax( int numberlist[], int n, int *p_min, int *p_max ){
  24.  
  25.   int min2, max2, i;
  26.  
  27.   if( n == 1 ) *p_min = *p_max = numberlist[0];
  28.  
  29.   else if( n == 2 ) {
  30.  
  31.     if( numberlist[0] < numberlist[i] ) {
  32.       *p_min = numberlist[0];
  33.       *p_max = numberlist[1];
  34.  
  35.     } else {
  36.       *p_min = numberlist[1];
  37.       *p_max = numberlist[0];
  38.     }
  39.  
  40.   } else {
  41. minmax( numberlist, n / 2, p_min, p_max );
  42.     minmax( numberlist + n / 2, n - ( n / 2 ), &min2, &max2 );
  43.  
  44.     if( min2 < *p_min )
  45.       *p_min = min2;
  46.  
  47.     if( max2 > *p_max )
  48.       *p_max = max2;
  49.   }
  50. }
Last edited by Dewey1040; Mar 30th, 2009 at 11:03 am.
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Re: minmax

 
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  #2
Mar 30th, 2009
This is where you went wrong.

In your program pointers min and max are there but are not pointing to any memory space at all.So when you try to access some memory as *min or *max they try to refer a memory not been allocated hence segmentation fault core dumped.

Try this:
c Syntax (Toggle Plain Text) 
  1. int main( int argc, char *argv[] ){
  2.  
  3. int *numberlist, i, n, *min, *max ,minimum,maximum;
  4.  
  5. min=&minimum;
  6. max=&maximum;
  7. //Followed by your code

By this you will have allocated the memory and then accessing it so no problem. And ya your max and min values will be in maximum and minimum.
Last edited by csurfer; Mar 30th, 2009 at 1:50 pm.
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Re: minmax

 
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  #3
Mar 30th, 2009
thanks csurfer, ill try that as soon as putty chooses to work again
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Re: minmax

 
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  #4
Mar 30th, 2009
Purely for the sake of simplicity, I would go with this route (doesn't use a second set of variables):

C Syntax (Toggle Plain Text) 
  1. int main( int argc, char *argv[] ){
  2.   int *numberlist, i, n, min, max ;
  3.  
  4.   n = atoi( argv[1] );
  5.   numberlist = ( int * ) malloc( n * sizeof( int ) );
  6.   for( i = 0; i < n; i++ ) numberlist[i] == rand() % n ;
  7.  
  8.   minmax( numberlist, n, &min, &max );
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Re: minmax

 
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  #5
Mar 30th, 2009
Think about another approach:
c Syntax (Toggle Plain Text) 
  1. struct IntRange { int minval, maxval; };
  2.  
  3. struct IntRange MinMax(const int* arr, int n)
  4. {
  5.     struct IntRange range = { 0, 0 };
  6.     if (arr && 0 < n) {
  7.         int i;
  8.         range.minval = range.maxval = arr[0];
  9.         for (i = 1; i < n; ++i) {
  10.             if (arr[i] < range.minval)
  11.                 range.minval = arr[i];
  12.             else if (range.maxval < arr[i])
  13.                 range.maxval = arr[i];
  14.         }
  15.     }
  16.     return range;
  17. };
  18.  
  19. int main()
  20. {
  21.     int* numberlist;
  22.     struct Range range;
  23.     ...
  24.     range = MinMax(numberlist,n);
  25.     printf("Min %d\nMax %d\n",range.minval.range.maxval);
  26. 	return 0;
  27. }
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Re: minmax

 
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  #6
Mar 30th, 2009
i have to use that function minmax because that is the one that we were assigned to use for the class, and i made the changed death oclock gave, but it just prints out the min and max values are 0... any ideas?
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Re: minmax

 
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  #7
Mar 30th, 2009
Ark's approach is much neater and most likely works. Your solution is very hard to read; the looping approach makes more sense.
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Re: minmax

 
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  #8
Mar 31st, 2009
heres my iterative method, the full assigment is to test the recursive method, and iterative method to see when the recursive method begins to be faster then the iterative method. (time both with array sizes of 500, 5000, 50000, 500000 numbers). And at the moment this one also only prints out the min and max values are 0.

C Syntax (Toggle Plain Text) 
  1. /*********************************************************************/
  2. /* iterminmax.c                                                       */
  3. /*********************************************************************/
  4.  
  5. #include <stdio.h>
  6. #include <stdlib.h>
  7.  
  8. void minmax( int a[], int n, int *p_min, int *p_max );
  9.  
  10. int main( int argc, char *argv[] ){
  11.  
  12.   int *numberlist, i, n, min, max;
  13.  
  14.   n = atoi( argv[1] );
  15.  
  16.   numberlist = ( int * ) malloc( n * sizeof( int ) );
  17.  
  18.   for( i = 0; i < n; i++ ) numberlist[i] == rand() % n ;
  19.  
  20.   minmax( numberlist, n, &min, &max );
  21.  
  22.   printf( "\nThe minimum value in your array is: %d", min );
  23.   printf( "\nThe maximum value in your array is: %d\n", max );
  24.  
  25.  
  26.   return 0;
  27. }
  28.  
  29. void minmax( int a[], int n, int *p_min, int *p_max ){
  30.  
  31.   int i;
  32.  
  33.   *p_max = *p_min = a[0];
  34.  
  35.   for( i = 1; i < n; i++ ){
  36.  
  37.     if( a[i] > *p_max )
  38.       *p_max = a[i];
  39.  
  40.     if( a[i] < *p_min )
  41.       *p_min = a[i];
  42.   }
  43. }
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Re: minmax

 
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  #9
Mar 31st, 2009
Look at csurfer's post again!
It was the true solution of your problems (in other words, it was a correction of your mistake )...
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Re: minmax

 
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  #10
Mar 31st, 2009
There is an initialization failure ...
  for( i = 0; i < n; i++ ) numberlist[i] == rand() % n ;
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