C lang DS

guides/C lang/Stacks.md

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+## Stacks
+Stacks is an ordered list in which insertions or if we say in normal words push or elements can be added,deletion or other functions like display can be done.
+
+* Stack follows LIFO rule that means Last In First Out in simple terms, whatever comes at the last is removed first.
+* Stack mainly has three functions-pop,push and display
+* Stack can be implemented by arrays,linked list(singly,doubly,circular) or even using queue
+* Stack is helpful in UNDO/REDO functions in editors and alll
+
+
+
+### A simple stack implementation using C lang
+
+ ```
+     #include <stdio.h>
+#include <stdlib.h>
+
+struct node{
+     int data;
+     struct node *next;
+}*start=NULL;
+
+void push(int x){
+     struct node *p;
+     p=(struct node *)(malloc(sizeof(struct node)));
+     // t=(struct node *)(malloc(sizeof(struct node)));
+     p->data=x;  
+     p->next=start;
+   start=p;
+
+}
+
+
+
+
+void display(){
+     struct node *t;
+      t=(struct node *)(malloc(sizeof(struct node)));
+      t=start;
+      if(t==NULL){
+          printf("Stack is empty");
+          return;
+      }
+      else{
+          while(t!=NULL){
+               printf("\t %d",t->data);
+               t=t->next;
+          }
+      }
+}
+
+
+
+void pop() {
+    if (start == NULL) {
+        printf("Stack is empty\n");
+        return ;
+    } else {
+        struct node *p = start;
+        int m = p->data;
+        start = start->next;
+        free(p);
+        printf("Popped element is %d",m);
+    }
+}
+
+
+
+
+
+     int main() {
+    int choice = 0;
+
+    while (choice != 4) {
+        printf("\nEnter a choice\n");
+        printf("\n 1. POP");
+        printf("\n 2. PUSH");
+        printf("\n 3. DISPLAY");
+        printf("\n 4. EXIT\n");
+        scanf("%d", &choice);
+
+        switch (choice) {
+            case 1: pop();
+                break;
+            case 2:
+                printf("Enter an element to push\n");
+                int el;
+                scanf("%d", &el);
+                push(el);
+                break;
+            case 3:
+                display();
+                break;
+            case 4:
+                printf("\nExiting program");
+                break;
+            default:
+                printf("Enter a valid choice");
+                break;
+        }
+
+}
+
+
+return 0;
+}
+
+```
+
+* In the above code snippet, it is a menu driven program that implements the basic functions of Stack