User defined values aren't honored in program at later points - c

Question

In the code below, the user is supposed to be able to define what nurses won't be available for work that week. The user has a list of the names, and they are supposed to type a number that corresponds to the name. Once that value is stored into the slackers[4] array, it should be using those user supplied values to remove those nurses from being selected come making selections. It doesn't seem to be honoring those selected values, despite avail_nurses[9] having the correct values at any point in time (I tested using printf statements).
Everything seems to be in good shape except that essential piece of the puzzle. I would appreciate some constructive critique and useful suggestions. If you can avoid it, don't write the code for me--I gotta learn somehow. Thanks in advance!
#include "stdafx.h"
#include <stdlib.h>
#include <time.h>
char *names[] = { "Denise", "Inja", "Jane", "Karen", "Maggie", "Margaret", "MJ", "Queen", "Sherri", NULL }; //ptr for names, 9 nurses
/*0 = Denise, 1 = Inja, 2 = Jane, 3 = Karen, 4 = Maggie, 5 = Margaret, 6 = MJ, 7 = Queen, 8 = Sherri*/
const char days[5][10] = { "Monday", "Tuesday", "Wednesday", "Thursday", "Friday" };
int randomNurse();
#define total_nurses 9 //number of nurses on staff
#define days_in_week 5 //number of work days in a week
int main() {
srand(time(NULL));
int day, pos, rand_num, i, j;
int slackers[4] = { 0, 0, 0, 0 }; //array that holds the selections for who isn't working
int avail_nurses[total_nurses] = { 1, 1, 1, 1, 1, 1, 1, 1, 1 }; //holds the status of each nurse, 0 = unavailable, 1 = available
/*this allows the user to repeat the program easily! flag determines if we run the program multiple times*/
while (char flag = 'y') {
/*prints names */
int temp_counter = 1; //counter
char **name_ptr = names;
while (*name_ptr) {
printf("%i) %s\n", temp_counter, *name_ptr);
name_ptr++;
temp_counter++;
}
/*this assumes that no more than FOUR nurses will be away on any given week*/
printf("\nEnter numbers that correspond to the nurses who won't be available for the week.\nType up to four numbers, each separated by a space.\n");
printf("When you are done, press \"Enter\".\n");
printf("If less than four nurses will be on leave, type a \"0\" in place of a selection.\n");
printf("Example: 1 2 5 0\n\n\n");
/*week selection of unavailable nurses*/
do {
printf("Who won't be here? ");
} while (scanf("%i %i %i %i", &slackers[0], &slackers[1], &slackers[2], &slackers[3]) != 4);
/*checks the selections made, and sets the available nurses to the correct value, zero if they are slacking||vacationing*/
for (int n = 0; n < 4; n++) {
int slacker = slackers[n];
if (slacker >= 1 && slacker <= 9)
avail_nurses[slacker - 1] = -1;
}
/*-----WEEKLY_ASSIGNMENT-----*/
int pos_per_day[days_in_week] = { 5, 9, 9, 8, 5 }; //number of nurses needed each day
int selection[days_in_week][total_nurses]; //the selected nurses per day
for (i = 0; i < days_in_week; i++) {
for (j = 0; j < total_nurses; j++) {
selection[i][j] = -1; //initialize to -1 which means no nurse is selected
}
}
//fill all the days of week
for (day = 0; day < days_in_week; day++) {
for (pos = 0; pos < pos_per_day[day]; pos++) { //for every position needed that day
do {
rand_num = randomNurse();
} while (!avail_nurses[rand_num]); //looks for available nurses (phrasing)
avail_nurses[rand_num] = 0; //change nurses status to not available
selection[day][pos] = rand_num; //fill the output array with appropriate nurse
}
for (i = 0; i < total_nurses; i++) {
avail_nurses[i] = 1; //initialize the nurses status for next day use
}
for (int n = 0; n < 4; n++) { //make sure we shame the slackers...
int slacker = slackers[n];
if (slacker >= 1 && slacker <= 9)
avail_nurses[slacker - 1] = -1;
}
/*DEBUGGING PRINTFs
printf("\n\nSELECTION:\n");
for (int x = 0; x < days_in_week; x++) {
for (int y = 0; y < total_nurses; y++) {
printf("%i\t", selection[x][y]);
}
printf("\n");
}*/
}
printf("\n");
/*-----PRINTS SCHEDULE FOR WEEK-----*/
for (i = 0; i < days_in_week; i++) {
printf("%-10s: ", days[i]);
for (j = 0; j < total_nurses; j++) {
if (selection[i][j] != -1)
printf("%-10s ", names[selection[i][j]]);
}
printf("\n");
}
fflush(stdin);
/*asks user if they want the program to run again*/
printf("\n\nDo you want to run the program again? (y/n) ");
scanf("%c", &flag);
if (flag == 'n' || flag == 'N') {
printf("\n");
break;
}
else {
printf("\n\n\n");
continue;
}
}
return 0;
}
/*function to generate random nurse*/
int randomNurse() {
return rand() % 9; //random number 0-8, to pick nurse
}

Answer 1

Your avail_nurses array uses the value 1 to indicate a nurse that's available, the value 0 to indicate a nurse that's not available as that nurse has already been assigned, and -1 to indicate a nurse that's not available because that nurse is a slacker. You then test whether or not a nurse is available with !avail_nurses[rand_num]. This statement is true if avail_nurses[rand_num] is 0 and is false if it's any other value. The means when avail_nurses[rand_num] is -1 it will exit the loop just like it does when it's 1.
To fix this bug either change the test to avail_nurses[rand_num] <= 0 or use only 0 to indicate unavailable nurses regardless of the reason why.