que.c

/* Que implementation using linked list */
#include <stdio.h>
#include <stdlib.h>

struct node {
    int data;
    struct node *next;
};

struct node *createNode(int data) {
    struct node *n = malloc(sizeof(struct node));
    n->data = data;
    n->next = NULL;
    return n;
}

struct que {
    struct node *rear;
    struct node *front;
};

struct que *createQue() {
    struct que *q = malloc(sizeof(struct que));
    q->rear = q->front = NULL;
    return q;
}

void enQue(struct que *q, int data) {
    struct node *n = createNode(data);
    if (q->front == NULL) {
        q->rear = q->front = n;
    } else {
        q->rear->next = n;
        q->rear = n;
    }
}

int deQue(struct que *q) {
    if (q->front == NULL) {
        printf("Error: que empty cannot deQue()\n");
        return 1;
    }
    struct node *n = q->front;
    int data = n->data;
    q->front = q->front->next;
    free(n);
    return data;
}

void printQue(struct que *q) {
    if (q->front == NULL) {
        printf("Error: que empty cannot printQue()\n");
        return;
    }
    struct node *n = q->front;
    while (n) {
        printf("%d ", n->data);
        n = n->next;
    }
    printf("\n");
}

int main(void) {
    struct que *q = createQue();

    enQue(q, 3);
    enQue(q, 30);
    enQue(q, 13);
    printQue(q);

    deQue(q);
    printQue(q);

    return 0;
}