I'm making simple patient managing program using circular queue but q.rear
always have "0" value while executing exit_hos()
I thought that addq()
makes variable "rear" different, but It doesn't work.
is_empty()
always return front and rear is same.
I think I'm misunderstanding some codes and memory concepts.
how can I fix these functions?
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_SIZE 50
#define MAX_QUEUE_SIZE 6
typedef struct {
char** value;
int front;
int rear;
} Queue;
void init_queue(Queue* q) {
q->value = (char**)malloc(sizeof(char*) * MAX_QUEUE_SIZE);
q->front = 0;
q->rear = 0;
}
int is_full(Queue* q) {
if (((q->rear +1) % MAX_QUEUE_SIZE) == q->front)
return 1;
else
return 0;
}
int is_empty(Queue* q) {
if (q->front == q->rear)
return 1;
else
return 0;
}
void addq(Queue* q, char* value) {
q->rear = (q->rear+1) % MAX_QUEUE_SIZE;
q->value[q->rear] = value;
printf("addq: %s", value);
return;
}
char* deleteq(Queue* q) {
q->front = (q->front + 1) % MAX_QUEUE_SIZE;
return q->value[q->front];
}
void arrive(Queue q) {
int input;
char name[MAX_SIZE];
printf("\n");
printf("1. submit\n");
printf("2. cancel\n");
scanf("%d", &input);
if (input == 1) {
if (is_full(&q) == 1) {
printf("Service is not available\n");
}
else {
printf("name: ");
scanf("%s", name);
addq(&q, name);
}
}
else if (input == 2) {
return;
}
else {
printf("input error\n");
return;
}
return;
}
void exit_hos(Queue q) {
char patient[MAX_SIZE];
if (is_empty(&q) == 1)
{
printf("There is no patient waiting\n");
}
else {
strcpy(patient, deleteq(&q));
printf("patient: %s", patient);
}
return;
}
int main() {
int input;
Queue q;
init_queue(&q);
while (1)
{
printf("\nINPUT\n");
printf("1. Arrive hostpital\n");
printf("2. Exit hospital\n");
printf("3. service exit\n");
scanf("%d", &input);
if (input == 1)
arrive(q);
else if (input == 2) {
exit_hos(q);
}
else if (input == 3) {
printf("exit\n");
return 0;
}
else {
printf("input error\n");
}
}
free(q.value);
return 0;
}
I think that this line is wrong:
q->value = (char**)malloc(sizeof(char*) * MAX_QUEUE_SIZE);
I think that it should be:
malloc is going to return a pointer to a char array.
q->value
is a pointer to a pointer to a char array. So you want to set it to the address of the char array that malloc is created for you.Change you
init_queue
code to this and it will work:Output: