/*  MeanvalueFunction.c  (c) Kari Laitinen

    http://www.naturalprogramming.com/

    2013-11-26 File created.
    2013-11-26 Last modification.
*/

#include  <stdio.h>

#define   ARRAY_SIZE     100

void read_array_of_numbers( double array_of_numbers[],
                            int*   number_of_numbers_in_array )
{
   int      number_index  =  0  ;
   double   number_from_keyboard   ;

   printf( "   Enter a number: " ) ;

   while ( ( scanf( "%lf", &number_from_keyboard ) )  &&
           ( number_index  <  ARRAY_SIZE    )  )
   {
      array_of_numbers[ number_index ]  =  number_from_keyboard ;
      number_index  ++ ;
      printf( "   Enter a number: " ) ;
   }

   *number_of_numbers_in_array  =  number_index ;
}


void calculate_mean_value( double array_of_numbers[],
                           int    number_of_numbers_in_array,

                           double* calculated_mean_value )
{
   double  sum_of_numbers   =  0  ;

   int number_index ;

   for ( number_index  =  0 ;
         number_index  <  number_of_numbers_in_array ;
         number_index  ++ )
   {
      sum_of_numbers  =  sum_of_numbers  +
                          array_of_numbers[ number_index ] ;
   }

   if ( number_of_numbers_in_array  >  0 )
   {
      *calculated_mean_value  = (double) sum_of_numbers /
                                (double) number_of_numbers_in_array ;
   }
   else
   {
      *calculated_mean_value  =  0 ;
   }
}

int main()
{
   double  array_of_numbers[ ARRAY_SIZE ] ;
   int     number_of_numbers_read ;
   double  mean_value ;

   printf( "\n This program calculates the mean value of"
           "\n the numbers that you enter from the keyboard."
           "\n The program stops when you enter a letter. \n\n" ) ;

   read_array_of_numbers( array_of_numbers,
                          &number_of_numbers_read ) ;

   calculate_mean_value( array_of_numbers,
                         number_of_numbers_read,

                         &mean_value ) ;

   printf( "\n The mean value is: %f\n", mean_value ) ;
}