Implemented in cpp for 3 exercises

Exercise_1.cpp

@@ -1,5 +1,5 @@
-#include <bits/stdc++.h> 
-  
+#include <iostream> 
+#include<bits/stdc++.h>
 using namespace std; 
 
 #define MAX 1000 
@@ -12,7 +12,9 @@ class Stack {
 public: 
     int a[MAX]; // Maximum size of Stack 
 
-    Stack() { //Constructor here } 
+    Stack() { 
+        top = -1;
+    } 
     bool push(int x); 
     int pop(); 
     int peek(); 
@@ -21,24 +23,36 @@ class Stack {
 
 bool Stack::push(int x) 
 { 
-    //Your code here
-    //Check Stack overflow as well
+    top++;
+    a[top]=x;
+    return true;
 } 
 
 int Stack::pop() 
 { 
-    //Your code here
-    //Check Stack Underflow as well 
+    if(top==-1){
+        std::cout<<"Stack Underflow";
+        return 0;
+    }
+    int topElement=a[top];
+    top--;
+    return topElement;
 } 
 int Stack::peek() 
 { 
     //Your code here
     //Check empty condition too
+    if(top==-1){
+        cout<<"Stack is empty";
+        return 0;
+    }
+    return a[top];
 } 
 
 bool Stack::isEmpty() 
 { 
     //Your code here 
+    return top==-1;
 } 
 
 // Driver program to test above functions 

Exercise_2.cpp

@@ -1,4 +1,5 @@
 #include <bits/stdc++.h> 
+#include <iostream>
 using namespace std; 
 
 // A structure to represent a stack 
@@ -19,21 +20,37 @@ StackNode* newNode(int data)
 int isEmpty(StackNode* root) 
 { 
     //Your code here 
+    return root==NULL;
 } 
 
 void push(StackNode** root, int data) 
 { 
     //Your code here 
+    StackNode* node = newNode(data);
+    node->next=*root;
+    *root=node;
 } 
 
 int pop(StackNode** root) 
 { 
     //Your code here 
+    if(isEmpty(*root)){
+        cout<<"Stack is empty";
+        return 0;
+    }
+    int val = (*root)->data;
+    *root=(*root)->next;
+    return val;
 } 
 
 int peek(StackNode* root) 
 { 
     //Your code here 
+    if(isEmpty(root)){
+        cout<<"Stack is empty";
+        return 0;
+    }
+    return root->data;
 } 
 
 int main() 

Exercise_3.cpp

@@ -1,4 +1,5 @@
 #include <bits/stdc++.h> 
+#include <iostream>
 using namespace std; 
 
 // A linked list node (changes) 
@@ -21,6 +22,12 @@ void push(Node** head_ref, int new_data)
     /* 3. Make next of new node as head */ 
 
     /* 4. move the head to point to the new node */
+
+    Node* newNode = new Node();
+    newNode->data = new_data;
+    newNode->next = (*head_ref);
+    (*head_ref) = newNode;
+
 }  
 
 /* Given a node prev_node, insert a new node after the given  
@@ -35,7 +42,16 @@ void insertAfter(Node* prev_node, int new_data)
 
     /* 4. Make next of new node as next of prev_node */
 
-    /* 5. move the next of prev_node as new_node */ 
+    /* 5. move the next of prev_node as new_node */
+    if(prev_node==NULL){
+        cout<<"Previous node cannot be null";
+        return;
+    }
+    Node* newNode = new Node();
+    newNode->data = new_data;
+
+    newNode->next = prev_node->next;
+    prev_node->next = newNode;
 }  
 
 /* Given a reference (pointer to pointer) to the head  
@@ -56,13 +72,31 @@ void append(Node** head_ref, int new_data)
     /* 5. Else traverse till the last node */
 
     /* 6. Change the next of last node */ 
+    Node* newNode = new Node();
+    newNode->data = new_data;
+    newNode->next = NULL;
+    if(*head_ref==NULL){
+        (*head_ref) = newNode;
+        return;
+    }
+    Node* ptr = *head_ref;
+    while(ptr->next){
+        ptr = ptr->next;
+    }
+    ptr->next = newNode;
+
 }  
 
 // This function prints contents of 
 // linked list starting from head  
 void printList(Node *node)  
 {  
     //Your code here
+    Node* ptr = node;
+    while(ptr){
+        cout<<ptr->data<<" ";
+        ptr = ptr->next;
+    }
 }  
 
 /* Driver code*/