Question

this code is about implementing stacks , I want for someone to rewrite it totally in different way

#include <iostream>
#include <stdexcept>
#include <vector>
#include <cstdlib>
using namespace std;

class Stack {
    public:
        bool isEmpty();
        // returns true if stack has no elements stored

        int top();
        // returns element from top of the stack
        // throws runtime_error("stack is empty")

        int pop();
        // returns element from top of the stack and removes it
        // throws runtime_error("stack is empty")

        void push(int);
        // puts a new element on top of the stack

    private:
        vector<int> elements;
};

//member function definitions
bool Stack::isEmpty()
{
    return elements.empty();
}

int Stack::top()
{
    if(isEmpty())
        throw runtime_error("stack is empty");
    return elements.back();
}

int Stack::pop()
{
    if(isEmpty())
        throw runtime_error("stack is empty");
    int item = elements.back();
    elements.pop_back();
    return item;
}

void Stack::push(int item)
{
    elements.push_back(item);
}
//member functions definitions end

int main()
{
    string line, cmd;
    int val;
    Stack stack;

    cout << "stack> ";
    //read line by line
    while(getline(cin, line))
    {
        //get the command

        //trim leading whitespace
        if(line.find_first_not_of(" \t") == string::npos)
        {
            // empty line
            cout << "stack> ";
            continue;
        }
        line = line.substr(line.find_first_not_of(" \t"));
        cmd = line.substr(0, line.find(" "));
        if(cmd == "push")
        {
            // remaining string
            line = line.substr(line.find(" ") + 1);
            if(line.size() == 0
                    || ( (line[0] == '-' || line[0] == '+') && line.find_first_of("0123456789") > 1)
                    || line.find_first_not_of("0123456789+-") == 0)
            {
                cout << "error: not a number" << endl;
            }
            else
            {
                val = atoi(line.c_str());
                stack.push(val);
            }
        }
        else if(cmd == "pop")
        {
            try
            {
                val = stack.pop();
                cout << val << endl;
            }
            catch(runtime_error& e)
            {
                cout << "error: " << e.what() << endl;
            }
        }
        else if(cmd == "top")
        {
            try
            {
                val = stack.top();
                cout << val << endl;
            }
            catch(runtime_error& e)
            {
                cout << "error: " << e.what() << endl;
            }
        }
        else if(cmd == "list")
        {
            Stack s2;
            bool first = true;
            cout << "[";
            /* pop repeatedly and store in another stack */
            while(! stack.isEmpty())
            {
                val = stack.pop();
                s2.push(val);
                if(!first)
                    cout << ",";
                cout << val;
                first = false;
            }
            cout << "]" << endl;
            /* restore original stack */
            while(! s2.isEmpty())
            {
                stack.push(s2.pop());
            }
        }
        else if(cmd == "end")
        {
            break;
        }
        else
        {
            cout << "error: invalid command" << endl;
        }

        cout << "stack> ";
    }

    cout << endl;
}

Answer 1

In given code, there is class named as "Stack" declared and all operations of stack data structure are

implemented by using vector.

Refer following different code is about implementing stacks:

#include <iostream>
using namespace std;

int stack[5];
int n=5;
int top=-1;

void push(int val) {
if(top>=n-1)
cout<<"Stack Overflow"<<endl;
else {
top++;
stack[top]=val;
}
}
void pop() {
if(top<=-1)
cout<<"Stack underflow"<<endl;
else {
cout<<"The popped element is "<< stack[top] <<endl;
top--;
}
}
void display() {
if(top>=0) {
cout<<"All elements of stack are:";
for(int i=top; i>=0; i--)
cout<<stack[i]<<" ";
cout<<endl;
} else
cout<<"Stack is empty"<<endl;
}
int main() {
int ch, val;
do {
cout<<"1) Push element in stack"<<endl;
cout<<"2) Pop element from stack"<<endl;
cout<<"3) Display stack elements"<<endl;
cout<<"4) Exit"<<endl;

cout<<"Enter your choice: "<<endl;
cin>>ch;
switch(ch) {
case 1: {   
cout<<"Enter value to push into stack:"<<endl;
cin>>val;
push(val);
break;
}
case 2: {
pop();
break;
}
case 3: {
display();
break;
}
case 4: {
cout<<"Exit"<<endl;
break;
}
default: {
cout<<"Invalid Choice"<<endl;
}
}
}while(ch!=4);
return 0;
}

In this code, there is no any class declaration and all operations of stack data structure is implemented by using Array.

This is menu driven program. I hope, you will understand.