1 files changed, 120 insertions, 0 deletions
diff --git a/data_structures/chapter_3/stack.c b/data_structures/chapter_3/stack.c
new file mode 100644
index 0000000..a27869f
--- /dev/null
+++ b/data_structures/chapter_3/stack.c
@@ -0,0 +1,120 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "stack.h"
+
+/* Stack implementation is a linked list with a header */
+struct node
+{
+    elem data;
+    ptr_to_node next;
+};
+
+int is_empty(stack s)
+{
+    return s->next == NULL;
+}
+
+stack create_stack()
+{
+    stack s;
+
+    s = malloc(sizeof(struct node));
+    if(s == NULL)
+        printf("error");
+    make_empty(s);
+    return s;
+}
+
+void make_empty(stack s)
+{
+    if(s == NULL)
+        printf("must create a stack first");
+    else
+        while(!is_empty(s))
+            pop(s);
+}
+
+void push(elem x, stack s)
+{
+    ptr_to_node tmp;
+
+    tmp = malloc(sizeof(struct node));
+    if(tmp == NULL)
+        printf("out of space");
+    else {
+        tmp->data = x;
+        tmp->next = s->next;
+        s->next = tmp;
+    }
+}
+
+void pop(stack s)
+{
+    if(!is_empty(s)) {
+        ptr_to_node tmp = s->next;
+        s->next = s->next->next;
+        free(tmp);
+    } else
+        printf("Empty stack");
+}
+
+elem top(stack s)
+{
+//    if(is_empty(s))
+//        printf("empty stack");
+//    else
+//        return s->next->data;
+//
+//   return -1;
+//
+/* tune version */
+    if(!is_empty(s))
+        return s->next->data;
+
+    printf("empty stack");
+    return 0;
+}
+
+void print_stack(stack s)
+{
+    printf("--------\n");
+    while(!is_empty(s)) {
+        printf("   %d\n", s->next->data);
+        s = s->next;
+    }
+    printf("--------\n");
+}
+
+void test()
+{
+    stack s;
+    s = create_stack();
+    push(1, s);
+    push(2, s);
+    print_stack(s);
+
+    push(3, s);
+    push(4, s);
+    push(5, s);
+    print_stack(s);
+    printf("%d\n",top(s));
+
+    pop(s);
+    print_stack(s);
+
+    pop(s);
+    pop(s);
+    pop(s);
+    pop(s);
+    pop(s);
+    pop(s);
+
+    print_stack(s);
+}
+
+int main()
+{
+    test();
+    return 0;
+}