/* Program to locate employees paid more than a user-supplied threshold.
   Input: the name of the file with the employee data, and the threshold
          amount.  The file must contain names in the first 30 columns,
          then the salary as a float.  A final line containing only a '#'
          marks the end of the file.
*/

#include <stdio.h>
#include <stdlib.h>
#define TRUE (1)
#define FALSE (0)

/* Declaration for functions called in main:  */
FILE * file_open(char name[], char access_mode[]);
void process_file(FILE * fin, float threshold);

main() {
    FILE * fin;                 /* Declare the FILE pointer (1). */
    char filename[81];
    float threshold;

    /* Ask the user the name of the file with the data. */
    printf("Name of file to read? ");
    scanf("%80s", filename);

    /* Open the file (using our own function - see below) (2). */
    fin = file_open(filename, "r");

    /* Ask the user the salary threshold limit. */
    printf("Salary threshold amount? ");
    scanf("%f", &threshold);

    /* Read all the file data, displaying those above the threshold (3). */
    process_file(fin, threshold);

    /* Close the file (4). */
    fclose(fin);
    return 0;
}

/******* file_open *******
 Works like fopen, but checks for errors, and if so, stops with an
 error message.  */

FILE * file_open(char name[], char access_mode[]) {
    FILE * f;
    f = fopen(name, access_mode);
    if (f == NULL) { /* error? */
        /* Library function perror prints an informative message. */
        perror("Cannot open file");
        exit(EXIT_FAILURE); /* Terminate after printing error message. */
    }
    return f;               /* Only happens if fopen succeeded. */
}

/******* process_file *******
On entry: fin refers to a file opened for input.  It must contain
          names and salaries.  The name must occupy the first 30
          chars of the line.  The last line starts with '#'.
On exit:  Will have listed all lines with salary greater than the
          threshold.  Prints a heading before the first such line,
          or an informative message if none are found.  No error
          checking is done.
*/
#define NAME_SIZE (30)

void process_file(FILE * fin, float threshold) {
    int no_previous_listings = TRUE;  /* Used to decide when to
                                         print the heading etc. */
    char employee_name[NAME_SIZE + 1];
    float salary;

    /* Load the first name */
    fgets(employee_name, NAME_SIZE+1, fin);

    while (employee_name[0] != '#') {  /* does not start with "#" */
        /* Load salary and following character (to skip the '\n') */
        fscanf(fin, "%f%*c", &salary);
        /* Decide whether to print. */
        if (salary>threshold) {
            if (no_previous_listings) {  /* Do we need headings? */
                printf("Staff with salary over $%4.2f:\n", threshold);
                printf(
                    "Name%*sSalary\n====%*s======\n",
                    NAME_SIZE-4, " ",
                    NAME_SIZE-4, " "
                );
                no_previous_listings = FALSE;
            }
            printf("%*s$%4.2f\n", NAME_SIZE, employee_name, salary);
        }

        /* Load the next name */
        fgets(employee_name, NAME_SIZE+1, fin);
    }

    /* Check whether anything was printed. */
    if (no_previous_listings) {
        printf("No staff have salaries over $%4.2f\n", threshold);
    }
}