Stack in Data Structure and algorithm :

What is Stack?

A stack is a linear data structure that follows the LIFO Principle.
LIFO means = Last In First Out
A stack can be defined as a container in which insertion and deletion can be performed from the one end known as the top of the stack.






Real-Life Example of Stack :

This is a real-life example of a stack.




Standard Stack Operations :

o push(): When we insert an element in a stack then the operation is known as a push. If the stack is full then the overflow condition occurs.
o pop(): When we delete an element from the stack, the operation is known as a pop. If the stack is empty means that no element exists in the stack, this state is known as an underflow state.
o isEmpty(): It determines whether the stack is empty or not.
o isFull(): It determines whether the stack is full or not.'
o peek(): It returns the element at the given position.
o count(): It returns the total number of elements available in a stack.
o change(): It changes the element at the given position.
o display(): It prints all the elements available in the stack.



Stack Implementation Using Array

PUSH Algorithm :

o Step 1: Checks if the Stack is full

o Step 2: If the stack is full, Produce an error and exit.

o Step 3: If the stack is not full, increments top to point next empty space.

o Step 4: Adds data element to the stack location, where top is pointing.

o Step 5: Return success




begin procedure push: stack, data

   if stack is full
      return null
   endif
   
   top ← top + 1
   stack[top] ← data

end procedure

Push Function Code :

void push(int data) {
    if(!isFull()) {
        top = top + 1;
        stack[top] = data;
    } else {
        printf("Stack is full.\n");
    }
}
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Here we have used isFull() Function, Let's see what is isFull() function algorithm



isFull Algorithm:


begin procedure isfull

        if top equals to MAXSIZE
           return true
        else
           return false
        endif
        
end procedure

isFull Function Code:

bool isfull() {
    if(top == MAXSIZE)
        return true;
    else
        return false;
}
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let's see whether my stack is empty or not 樂

isEmpty Function Algorithm:

begin procedure isempty

        if top less than 1
           return true
        else
           return false
        endif
        
end procedure

isEmpty Function code:

bool isempty() {
    if(top == -1)
        return true;
    else
        return false;
}
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Now let's see the pop operation and it's an algorithm

Pop Operations :


o Step 1: Checks if the Stack is full

o Step 2: If the stack is empty, produces an error and exit

o Step 3: If the stack is not empty, accesses the data element at which top is pointing.

o Step 4: Decreases the value of top by 1.

o Step 5: Return success




Pop Algorithm: 


begin procedure pop: stack

        if stack is empty
           return null
        endif
        
        data ← stack[top]
        top ← top - 1
        return data
     
end procedure

Pop Function Code :


int pop(int data) {
    if(!isempty()) {
        data = stack[top];
        top = top - 1;
        return data;
    } else {
        printf("Stack is empty.\n");
    }
}
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Peek Algorithm :

Now if I want to know the top element or you can say peek element then ? 樂

Let's see


begin procedure peek
    return stack[top]
end procedure

Peek Function Code : 

int peek() {
    return stack[top];
}
C++