Issues with a char stack implementation in c++? - c++

I want to make a char stack implementation, but i think something is wrong with it because when i try to use it for my other function it does not word and library stack works. Can you help to find an issue:
using namespace std;
Stack::Stack(int size)
{
arr = new char[size];
capacity = size;
t = -1;
}
int Stack::size()
{
return (t + 1);
}
Stack::~Stack()
{
delete[] arr;
}
bool Stack::empty()
{
return size()==0;
}
void Stack::push(char x)
{
if (size()==capacity) {
cout<<"Push to full stack";
arr[++t]=x;
}
}
char Stack::pop()
{
if (empty()) {
cout<<"Pop from empty stack";
--t;
}
return 0;
}
char Stack::top()
{
if (!empty())
return arr[t];
else
cout<<"Top of the stack is empty";
return 0;
}
I want to make a char stack implementation, but i think something is wrong with it because when i try to use it for my other function it does not word and library stack works. Can you help to find an issue:
Thank you in advance!

I think you need to make some changes to the push and pop function for your Stack to work
In push, you should put arr[++t]=x; outside the if statement instead of inside as you want to add value to arr if the current size is less than its capacity instead of when it is equal
In pop, you should put arr[--t]; outside the if statement instead of inside as you want to remove and return the last value in the array if the stack is not empty. When it is empty, you should consider returning a default character such as the null terminator character \0. You should also want to use arr[t--] instead of arr[--t] as the last element is currently at t so you want it to evaluate arr[t] before decreasing its value (t--)
void Stack::push(char x)
{
if (size()==capacity) {
cout<<"Push to full stack";
return;
}
arr[++t]=x;
}
char Stack::pop()
{
if (empty()) {
cout<<"Pop from empty stack";
return '\0';
}
return arr[t--];
}

Related

How to reverse print stack using recursion?

Please note that it is just reverse printing not reversing a stack
What I want to do is with the help of recursion print the stack i.e bottom to top printing.
I have tried myself but the result is not what I expected.My code looks like this.
#include <bits/stdc++.h>
using namespace std;
void print(stack<char>st){
if(st.empty()){return;}
st.pop();
print(st);
cout<<st.top();
}
int main() {
// Assume that I have stack already made....
print(st);
cout<<endl;
}
return 0;
}
Would anybody mind having pointing out my mistake ? Also when I pass stack by reference the results are unexpected.Thanks for support.
Why don't you store the st.top() at variable and print it later.
void print(stack<char>st)
{
if(st.empty())
{
return;
}
char top = st.top();
st.pop();
print(st);
cout<<top<<endl;
}
Let me explain you:-
Suppose, Your stack --> 0, 1
Here, Call Hierarchy
print({0, 1})
{
// stack after pop -- {0}
print({0})
}
print({0})
{
// stack after pop -- {}
print ({})
// here you want to print top of empty stack
// which gives the exception
}
pop is function get element to print like reverse
void printStack()
{
if(!isEmpty())
{
int temp = pop();
printStack();
printf(" %d ", temp);
push( temp);
}
}
int pop()
{
if (isEmpty())
printf("Stack is Empty...\n");
else {
st.top = st.top - 1;
return st.array[st.top+1];
}
}

Implementation of stack in C++ without using <stack>

I want to make an implementation of stack, I found a working model on the internet, unfortunately it is based on the idea that I know the size of the stack I want to implement right away. What I want to do is be able to add segments to my stack as they are needed, because potential maximum amount of the slots required goes into 10s of thousands and from my understanding making the size set in stone (when all of it is not needed most of the time) is a huge waste of memory and loss of the execution speed of the program. I also do not want to use any complex prewritten functions in my implementation (the functions provided by STL or different libraries such as vector etc.) as I want to understand all of them more by trying to make them myself/with brief help.
struct variabl {
char *given_name;
double value;
};
variabl* variables[50000];
int c = 0;
int end_of_stack = 0;
class Stack
{
private:
int top, length;
char *z;
int index_struc = 0;
public:
Stack(int = 0);
~Stack();
char pop();
void push();
};
Stack::Stack(int size) /*
This is where the problem begins, I want to be able to allocate the size
dynamically.
*/
{
top = -1;
length = size;
z = new char[length];
}
void Stack::push()
{
++top;
z[top] = variables[index_struc]->value;
index_struc++;
}
char Stack::pop()
{
end_of_stack = 0;
if (z == 0 || top == -1)
{
end_of_stack = 1;
return NULL;
}
char top_stack = z[top];
top--;
length--;
return top_stack;
}
Stack::~Stack()
{
delete[] z;
}
I had somewhat of a idea, and tried doing
Stack stackk
//whenever I want to put another thing into stack
stackk.push = new char;
but then I didnt completely understand how will it work for my purpose, I don't think it will be fully accessible with the pop method etc because it will be a set of separate arrays/variables right? I want the implementation to remain reasonably simple so I can understand it.
Change your push function to take a parameter, rather than needing to reference variables.
To handle pushes, start with an initial length of your array z (and change z to a better variable name). When you are pushing a new value, check if the new value will mean that the size of your array is too small (by comparing length and top). If it will exceed the current size, allocate a bigger array and copy the values from z to the new array, free up z, and make z point to the new array.
Here you have a simple implementation without the need of reallocating arrays. It uses the auxiliary class Node, that holds a value, and a pointer to another Node (that is set to NULL to indicate the end of the stack).
main() tests the stack by reading commands of the form
p c: push c to the stack
g: print top of stack and pop
#include <cstdlib>
#include <iostream>
using namespace std;
class Node {
private:
char c;
Node *next;
public:
Node(char cc, Node *nnext){
c = cc;
next = nnext;
}
char getChar(){
return c;
}
Node *getNext(){
return next;
}
~Node(){}
};
class Stack {
private:
Node *start;
public:
Stack(){
start = NULL;
}
void push(char c){
start = new Node(c, start);
}
char pop(){
if(start == NULL){
//Handle error
cerr << "pop on empty stack" << endl;
exit(1);
}
else {
char r = (*start).getChar();
Node* newstart = (*start).getNext();
delete start;
start = newstart;
return r;
}
}
bool empty(){
return start == NULL;
}
};
int main(){
char c, k;
Stack st;
while(cin>>c){
switch(c){
case 'p':
cin >> k;
st.push(k);
break;
case 'g':
cout << st.pop()<<endl;
break;
}
}
return 0;
}

How to implement a dynamically resizable stack in C++?

my code right now is just a simple stack that has push, pop, and display methods. How can I change my stack so that the size of the stack dynamically resizes based on the number of elements entered? So, for example, if the stack is full, I create a new stack that is twice the size of the original, and copy the data to the new stack.
Thanks.
#include <iostream>
#include <stdexcept>
using namespace std;
class Stack
{
private:
int *p;
int top,length;
public:
Stack(int = 0);
~Stack();
void push(int);
int pop();
void display();
};
Stack::Stack(int size)
{
top=-1;
length=size;
while(length <= 0) //If the stack size is zero, allow user to mention it at runtime
{
cout<<"Stack of zero size"<<endl;
cout<<"Enter a size for stack : ";
cin >> length;
}
p=new int[length];
}
Stack::~Stack()
{
delete [] p;
}
void Stack::push(int elem)
{
if(top==(length-1)) //If the top reaches to the maximum stack size
{
throw overflow_error("Can't push onto a full stack");
}
else
{
top++;
p[top]=elem;
}
}
int Stack::pop()
{
if(top==-1)
{
throw underflow_error("Can't pop from an empty stack");
}
int ret=p[top];
top--;
length--;
return ret;
}
void Stack::display()
{
for(int i = 0; i <= top; i++)
cout<<p[i]<<" ";
cout<<endl;
}
int main()
{
int len;
cout<<"Enter a size for stack : ";
cin >> len;
Stack s1(len);
try{
s1.push(1);
s1.display();
s1.push(2);
s1.push(3);
s1.push(4);
s1.push(5);
s1.display();
s1.pop();
s1.display();
s1.pop();
s1.display();
s1.pop();
s1.display();
s1.pop();
s1.display();
s1.pop();
s1.display();
}
catch(overflow_error){
cerr<< "Illegal operation. Cannot push onto a full stack.";
return -1;
}
catch(underflow_error){
cerr<< "Illegal operation. Cannot pop from an empty stack.";
return -1;
}
}
void Stack::push(int elem)
{
if(top==(length-1)) //If the top reaches to the maximum stack size
{
int* newp = new int[length * 2];
std::memcpy(newp, p, sizeof(int) * length);
delete[] p;
p = newp;
top++;
p[top]=elem;
length*=2;
}
else
{
top++;
p[top]=elem;
}
}
The stack class in the standard library (std::stack) solves this by delegating to a container class such as std::vector. That's slightly cheating, though.
However, the idea behind std::vector<> is fairly straightforward and reusable. When you hit the maxiumum size, do the following things in order:
Allocate new memory. No big problem if it fails (no data lost)
Copy all existing elements over. Use std::uninitialized_copy not std::copy
Swap the new and old pointer
Delete the old objects
Free the old allocation
One simple way is to double the stack size each time pushing a new element would overflow the stack. In that instance, you detect the potential overflow and then you would use declare a new int array that is twice the size of the old one and then copy the old array into this new array and reassign the pointer to that new array and delete the old array. The are other more optimal ways, but that is a simplistic way of doing it, you can use up considerably more memory than is necessary to add the new item, but it's a lot faster than reallocating with every new item that would overflow your stack.
Instead of throwing the exception overflow_error("Can't push onto a full stack") you can allocate more memory using new and copy the contents to that memory and release the previously allocated memory(memory swapping).
void Stack::push(int elem)
{
if(top==(length-1)) //If the top reaches to the maximum stack size
{
//throw overflow_error("Can't push onto a full stack");
int *pTemp = new int[length + 10/*value u want to increment*/];
memcpy(p,pTemp,length); //for using this include stdlib
delete[] p;
p = pTemp;
}
top++;
p[top]=elem;
}

Why does this code crash while testing stack?

OK, so I edited my code, but I still have two problems :
But here's my code first :
#include <iostream>
using namespace std;
struct stack
{
int data[5];
int top;
};
void push (int a, stack &S)
{
S.top++;
if (S.top<5)
{
S.data[S.top]=a;
}
else cout<<"Stack is full!!!"<<endl; S.top--;
}
int pop(stack &S)
{
if (S.top==-1)
{
cout<<"Stack is empty!"<<endl;
}
else
{
int temp=S.data[S.top];
S.data[S.top]=NULL;
S.top--;
return temp;
}
}
bool isEMPTY(stack &S)
{
if (S.top==-1)
return true;
else return false;
}
bool isFULL(stack &S)
{
if (S.top==5)
return true;
else return false;
}
int main()
{
stack S = { {}, -1 };
push(5,S); cout<<"5 is pushed \n"<<endl;
push(3,S); cout<<"3 is pushed \n"<<endl;
push(1,S); cout<<"1 is pushed \n"<<endl;
push(2,S); cout<<"2 is pushed \n"<<endl;
push(6,S); cout<<"6 is pushed \n"<<endl;
push(7,S); cout<<"7 is pushed \n"<<endl;
cout<<pop(S)<<"is popped\n"<<endl;
cout<<pop(S)<<"is popped\n"<<endl;
cout<<pop(S)<<"is popped\n"<<endl;
return 0;
}
So, the first problem is, when I pop I get a "Totally random value" and it's not like LIFO.
Second is, I actually intended on inserting 6 values, when I already had the max value = 5, so the output actually showed me the 6 values.
stack S;
Since stack is POD, the above line doesn't initialize the member top. As such, using an uninitialized top in push and pop functions invokes undefined behavior.
Write this:
stack S {}; //must be compiled in C++11 mode, else write : stack S = stack();
This value-initializes S and its members, which means, top is initialized to 0. The rest of the code may still have other problems, but at least you have fixed the issues with proper initialization. If you work with 0 as initial value of top, you've write the logic of push and pop accordingly!
Once you fix that, check the value of top before pushing and poping values from the stack, as the member array can have at most 5 elements, and you cannot pop more elements when it is empty. You must maintain these invariants.
I do not see where an object of type stack was created and how data member top was initialized.
Also take nto account that member function push does not check whether there is an attempt to add an item beyond the array.
You should define the object the following way
stack S = { {}, -1 };
else cout<<"Stack is full!!!"<<endl; S.top--;
is identical to :
else
{
cout<<"Stack is full!!!"<<endl;
}
S.top--;
as a general rule, try to avoid: writing if/else without curly brackets, and, avoid writing more then one line of code in the same line.
The mistake is:
stack s;//you define the local variable "s" without been intitialized.
push(5,s);//pass the uninlitialized "s" to the function "push",when debugging your code,"s.top" is not a expected "-1",but some value incredible~(often extreamly larger than 5),so your push operation failed!
stack S;
S.top = -1;
for(int i = 0; i < 5; i++)
{
S.data[i] = 0;
}

error: request for member '..' in 'this', which is of non-class type '--* const'

My first ever question here. Please excuse me, I have just entered into C++ and was starting up with DS. STACK!!!
My code: I think
using namespace std;
typedef char stackElement;
class Stack
{
public:
stackElement *contents; //dynamically allocated: as we do not know what would be the size of our array.
int top, maxSize; // current Top index in the array
//max size of the array; we need it to know if the array is full
Stack(int maxSize)
{
contents = new stackElement(maxSize);
this.maxSize = maxSize;
if(contents == NULL)
{
cout<<"Insufficient memory";
exit(1);
}
top = -1;
}
~Stack()
{
delete [] contents;
contents = NULL;
maxSize = 0;
top = -1;
}
bool isEmpty()const
{
return top < 0;
}
bool isFull() const
{
return top == maxSize - 1;
}
void push(stackElement element)
{
if(isFull())
{
cout<<"STACK IS ALREADY FULL";
exit(1);
}
top = top + 1;
contents[top] = element;
}
};
int main()
{
cout<<"STACK IMPLEMENTATION";
int i = 1;
Stack s1(i);
s1.push('a');
s1.push('1');
return 0;
}
I am getting this error:
error: request for member 'maxSize' in 'this', which is of non-class type 'Stack* const'
If at all, you'd have to write this->maxSize = maxSize;, since this is a pointer.
But better not to write that at all and instead use the constructor-initializer list:
explicit Stack(int m)
: contents(new stackElement[m]), top(-1), maxSize(m)
{
// nothing else to do
}
I also added explicit so you don't accidentally convert 5 into a Stack.
You also wrote the array initialization wrong.
Also, you don't need to check that contents is not null: When new fails, it exits with an exception, it does not return a null pointer. (That behaviour would make no sense when you think in terms of objects.)
It is crucial to note that you have at most one naked new-expression in your constructor. Anything else is an exception-safety disaster, and a sign that you need to refactor and use single-responsibility resource-managing classes.
The destructor should just be: ~Stack() { delete [] contents; } Everything else is pointless waste.
Imagine you had to pay for every line of code you write. Be patient, lose the source, think.
Write
this->maxSize = maxSize;
instead of
this.maxSize = maxSize;
The this is a pointer type, not a reference type
this->maxSize instead of this.maxSize