Added data_structure queue.c

data_structures/queue.c

@@ -0,0 +1,75 @@
+////////////////////////////////////////////////////////////////////////////////
+//INCLUDES
+#include <stdio.h>
+#include <stdlib.h>
+
+////////////////////////////////////////////////////////////////////////////////
+//MACROS: CONSTANTS
+
+////////////////////////////////////////////////////////////////////////////////
+//DATA STRUCTURES
+struct node {
+    int data;
+    struct node* next;
+    struct node* pre;
+} *head, *tail, *tmp;
+
+////////////////////////////////////////////////////////////////////////////////
+//GLOBAL VARIABLES
+int count;
+
+////////////////////////////////////////////////////////////////////////////////
+//FORWARD DECLARATIONS
+void create();
+void enque(int x);
+int deque();
+int peek();
+int size();
+int isEmpty();
+
+////////////////////////////////////////////////////////////////////////////////
+//MAIN ENTRY POINT
+
+int main(int argc, char const *argv[]) {
+
+    create();
+    enque(5);
+
+
+	return 0;
+}
+
+
+void create() {
+    head = NULL;
+    tail = NULL;
+}
+
+void enque(int x) {
+    if(head == NULL) {
+        head = (struct node *)malloc(1 * sizeof(struct node));
+        head->data = x;
+        head->pre = NULL;
+        tail = head;
+    } else {
+        tmp = (struct node *)malloc(1 * sizeof(struct node));
+        tmp->data = x;
+        tmp->next = tail;
+        tail = tmp;
+    }
+}
+
+int deque() {
+    int returnData;
+    if(head == NULL) {
+        printf("ERROR: Deque from empty queue.\n");
+        exit(1);
+    } else {
+        returnData = head->data;
+        if(head->pre == NULL)
+            head = NULL;
+        else
+            head = head->pre;
+        head->next = NULL;
+    }
+}