From 9e9bd5c99aedb60f03dd36eec6ca13da0f888be5 Mon Sep 17 00:00:00 2001
From: VIJETA CHAVHAN <65402647+vijeta-2000@users.noreply.github.com>
Date: Thu, 28 Oct 2021 10:14:54 +0530
Subject: [PATCH] stack.c

---
 C/stack.c | 159 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 159 insertions(+)
 create mode 100644 C/stack.c

diff --git a/C/stack.c b/C/stack.c
new file mode 100644
index 0000000..5835b0c
--- /dev/null
+++ b/C/stack.c
@@ -0,0 +1,159 @@
+/**
+ * Stack data structure implementation.
+ */
+
+////////////////////////////////////////////////////////////////////////////////
+// INCLUDES
+#include <stdio.h>
+#include <stdlib.h>
+
+////////////////////////////////////////////////////////////////////////////////
+// MACROS: CONSTANTS
+
+////////////////////////////////////////////////////////////////////////////////
+// DATA STRUCTURES
+/**
+ * creating a stucture with 'data'(type:int), two pointers 'next','pre' (type: struct node) .
+ */
+struct node
+{
+    int data;
+    struct node *next;
+    struct node *pre;
+} * head, *tmp;
+
+////////////////////////////////////////////////////////////////////////////////
+// GLOBAL VARIABLES
+int count = 0;
+
+////////////////////////////////////////////////////////////////////////////////
+// FUNCTION PROTOTYPES
+void create();
+void push(int x);
+int pop();
+int peek();
+int size();
+int isEmpty();
+
+////////////////////////////////////////////////////////////////////////////////
+// MAIN ENTRY POINT
+
+int main(int argc, char const *argv[])
+{
+    int x, y, z;
+
+    create();
+    push(4);
+    x = pop();
+    // 4. Count: 0. Empty: 1.
+    printf("%d.\t\tCount: %d.\tEmpty: %d.\n", x, size(), isEmpty());
+
+    push(1);
+    push(2);
+    push(3);
+    x = pop();
+    y = pop();
+    // 3, 2. Count: 1. Empty: 0;
+    printf("%d, %d.\t\tCount: %d.\tEmpty: %d.\n", x, y, size(), isEmpty());
+    pop();  // Empty the stack.
+
+    push(5);
+    push(6);
+    x = peek();
+    push(7);
+    y = pop();
+    push(8);
+    z = pop();
+    // 1, 6, 7, 8. Count: 2. Empty: 0.
+    printf("%d, %d, %d.\tCount: %d.\tEmpty: %d.\n", x, y, z, size(), isEmpty());
+
+    return 0;
+}
+
+/**
+ * Initialize the stack to NULL.
+ */
+void create() { head = NULL; }
+
+/**
+ * Push data onto the stack.
+ */
+void push(int x)
+{
+    if (head == NULL)
+    {
+        head = (struct node *)malloc(1 * sizeof(struct node));
+        head->next = NULL;
+        head->pre = NULL;
+        head->data = x;
+    }
+    else
+    {
+        tmp = (struct node *)malloc(1 * sizeof(struct node));
+        tmp->data = x;
+        tmp->next = NULL;
+        tmp->pre = head;
+        head->next = tmp;
+        head = tmp;
+    }
+    ++count;
+}
+
+/**
+ * Pop data from the stack
+ */
+int pop()
+{
+    int returnData;
+    if (head == NULL)
+    {
+        printf("ERROR: Pop from empty stack.\n");
+        exit(1);
+    }
+    else
+    {
+        returnData = head->data;
+
+        if (head->pre == NULL)
+        {
+            free(head);
+            head = NULL;
+        }
+        else
+        {
+            head = head->pre;
+            free(head->next);
+        }
+    }
+    --count;
+    return returnData;
+}
+
+/**
+ * Returns the next value to be popped.
+ */
+int peek()
+{
+    if (head != NULL)
+        return head->data;
+    else
+    {
+        printf("ERROR: Peeking from empty stack.");
+        exit(1);
+    }
+}
+
+/**
+ * Returns the size of the stack.
+ */
+int size() { return count; }
+
+/**
+ * Returns 1 if stack is empty, returns 0 if not empty.
+ */
+int isEmpty()
+{
+    if (count == 0)
+        return 1;
+    return 0;
+}