1. Data Structures and Algorithms
Prof. Ajit A. Diwan
Prof. Ganesh Ramakrishnan
Prof. Deepak B. Phatak
Department of Computer Science and Engineering
IIT Bombay
Session: Stacks using STL
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay

2. The Stack Class Last in First Out (Push and Pop – Both from the top)
Container Adaptor
Must use #include<stack> at the beginning of the program
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay

3. The Stack Class: Member Functions
empty()
size()
top()
push()
pop()
swap()
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay

4. Program 1: Basic #include <iostream>
#include <stack>
#include <vector>
using namespace std;
int main () {
stack<char> s1;
stack<int,std::vector<int> > s2;
deque<float> d1(5,0.0);
stack<float> s3 (d1);
vector<char> v1(3,'a');
stack<char, vector<char> > s4 (v1);
cout << "Size of stacks: "
<< s1.size() << "\t"
<< s2.size() << "\t"
<< s3.size() << "\t"
<< s4.size() << endl;
return 0; }
Empty stack of characters
Empty stack of integers using vectors
Output
Size of stacks:
Stack of float type of size 5 and initialized to 0.0
Stack of characters of size 3 and initialized to a
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay

5. Program 2: Implement Stack
int main () {
stack<char> s1;
int i=0; char element='a';
if(s1.empty()==true)
cout << "Stack is empty as expected" << endl;
else
cout << "Stack is not empty" << endl;
for(i=0;i<=2;i++) {
s1.push(element);
cout<<"Element "<<element<<" pushed in"<<endl;
element++; }
cout << "Size of stack: " << s1.size() << endl;
Empty stack of characters
Since Stack is empty, Stack is empty as expected is printed
Element a pushed in
Element b pushed in
Element c pushed in
Size of stack: 3
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay

6. Program 2: Implement Stack (contd.)
while(s1.empty()!=true) {
cout << "Top element: " << s1.top() << endl;
s1.pop();
cout << "Element popped" << endl; }
if(s1.empty()==true)
cout << "Stack is empty" << endl;
else
cout << "Stack is not empty" << endl;
return 0;
Top element: c
Element popped
Top element: b
Top element: a
Since all elements are popped out, stack is empty
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay

7. What if stack was implemented using procedural approach?
Points to remember
Accessing ‘top’ when stack is empty
Popping elements exceeding the size of stack
What if stack was implemented using procedural approach?
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay

8. Stack: swap() Swaps contents of two stacks Should be of the same type
Size may be different
int main () {
stack<int> s1, s2;
int i=0;
for(i=0;i<=2;i++) { s1.push(i); }
for(i=0;i<=5;i++) { s2.push(i); }
cout << "Size of stacks : " << s1.size() << "\t" << s2.size() << endl;
swap(s1,s2);
return 0; }
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay

9. Thank you
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay