/***************************************************************************
 *  Usage:  sort input-file output-file
 *
 *  Sort a list of real numbers in input-file, placing the results
 *  in output-file.  Both input and output files contain one
 *  number per line.
 *
 *  Arguments:
 *  input-file:     file to be sorted
 *  output-file:    file to receive the sorted list
 *
 *  History: 
 *  Date        Name        Modification
 *  2017-08-24  Jason Bacon Begin
 ***************************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <sysexits.h>

double  *read_list(size_t *size, const char filename[]);
int     print_list(const double list[], size_t list_size, const char filename[]);
void    sort_list(double list[], size_t list_size);
void    usage(void);

int     main(int argc,char *argv[])

{
    double  *list;
    size_t  list_size;
    int     status = EX_OK;
    char    *input_file,        // Just for readability
            *output_file;
    
    if ( argc != 3 )
        usage();
    input_file = argv[1];
    output_file = argv[2];
    
    list = read_list(&list_size, input_file);
    if ( list == NULL )
    {
        perror(input_file);
        return EX_NOINPUT;
    }
    sort_list(list, list_size);
    if ( print_list(list, list_size, output_file) != EX_OK )
    {
        perror(output_file);
        status = EX_CANTCREAT;
    }
    free(list);
    return status;
}


/*
 *  Input list size, allocate array, and read in list.
 */

double  *read_list(size_t *size_ptr, const char filename[])

{
    size_t  c;
    double  *list = NULL;
    FILE    *input_file;
    
    /*
     *  If open fails, just return an error code to the caller.  This is a
     *  general-purpose function, usable in many programs, so it should not
     *  take any specific action.
     */
    input_file = fopen(filename, "r");
    if ( input_file != NULL )
    {
        fscanf(input_file, "%zu", size_ptr);    // No & here, since size_ptr is a pointer
        list = (double *)malloc(*size_ptr * sizeof(*list));
        for (c = 0; c < *size_ptr; ++c)
            fscanf(input_file, "%lf", &list[c]);
    }
    fclose(input_file);
    return list;
}

/*
 *  Print contents of a list to a file.
 */

int     print_list(const double list[], size_t list_size, const char filename[])

{
    size_t  c;
    FILE    *output_file;
    
    /*
     *  If open fails, just return an error code to the caller.  This is a
     *  general-purpose function, usable in many programs, so it should not
     *  take any specific action.
     */
    output_file = fopen(filename, "w");
    if ( output_file != NULL )
    {
        for (c = 0; c < list_size; ++c)
            fprintf(output_file, "%f\n", list[c]);
        return EX_OK;
    }
    fclose(output_file);
    return EX_CANTCREAT;
}


/*
 *  Sort list using selection sort algorithm.
 */

void    sort_list(double list[], size_t list_size)

{
    size_t  start,
            low,
            c;
    double  temp;
    
    for (start = 0; start < list_size - 1; ++start)
    {
        /* Find lowest element */
        low = start;
        for (c = start + 1; c < list_size; ++c)
            if ( list[c] < list[low] )
                low = c;
        
        /* Swap first and lowest */
        temp = list[start];
        list[start] = list[low];
        list[low] = temp;
    }
}


void    usage(void)
{
    fputs("Usage: selsort-files input-file output-file\n", stderr);
    exit(EX_USAGE);
}

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5.4
4.1
3.9
2.7