Array implementation of stack

Here will discuss the array implementation of stack.

Problems with array implementation
Underflow - Array may be empty but people may try to pop the element
Overflow - Array is full. To over come we have to use re-szing of array. We can see how we can solve this problem here - http://k2code.blogspot.com/2013/09/resizing-array-implementation-of-stack.html
Null items - Can nulls be added - Yes in this case, nulls can be added in stack
Loitering (java specific) - Holding a reference to an object wen it is no longer needed. To over come this we should explicitly set array index to null. For eg.

public string pop() //stack of string  
{  
  String item = stackArray\[--top\];  
  stackArray\[top\] = null;  
  return item;  
}  

```Doing so, makes your program less of memory consumer.  
**Stack in java**  
Following is the implementation of stack in java:  

public class MyStack {
private int maxSize;
private long[] stackArray;
private int top;
public MyStack(int s) {
maxSize = s;
stackArray = new long[maxSize];
top = -1;
}
public void push(long j) {
stackArray[++top] = j;
}
public long pop() {
return stackArray[top–];
}
public long peek() {
return stackArray[top];
}
public boolean isEmpty() {
return (top == -1);
}
public boolean isFull() {
return (top == maxSize - 1);
}
public static void main(String[] args) {
MyStack theStack = new MyStack(10);
theStack.push(10);
theStack.push(20);
theStack.push(30);
theStack.push(40);
theStack.push(50);
while (!theStack.isEmpty()) {
long value = theStack.pop();
System.out.print(value);
System.out.print(" “);
}
System.out.println(”");
}
}

Following is the implementation in cpp:  

#include <stdio .h>
#include <conio .h>
#define MAX 20
int top=-1,ch;
int a[MAX];
int main(){
void menu();
void push();
void pop();
void display();
menu();
while(ch!=3){
switch(ch){
case 1:
push();
display();
break;
case 2:
pop();
display();
break;
}
menu();
}
}
void push()
{
if(top==MAX-1)
printf(“Stack is full\nStack overflow\n”);
else
{
printf(“Enter element:”);
scanf("%d",&a[++top]);
}
}
void pop()
{
if(top==-1)
printf(“Stack is emplty\nSTACK UNDERFLOW\n”);
else
{
top–;
printf(“Deleted %d\n”,a[top+1]);
}
}
void display()
{
int i=0;
printf("\nStack is :\n");
for(i=top;i>=0;i–)
printf("%d\n",a[i]);
}
void menu()
{
printf("\n1.Push\n2.Pop\n3.Exit\n");
scanf("%d",&ch);
while(ch < 1 ch=>3)
{
printf(“Enter valid choice 1,2 or 3\n”);
scanf("%d",&ch);
}
}

  
**Stack Implementation in CPP** (using classes)  

#include
using namespace std;
#define STACKSIZE 10
class stack
{
private:
int arr[STACKSIZE+1];
int tos;
public:
stack();
void push(int x);
int pop();
bool is_empty();
bool is_full();
int size();
void display();
};
stack::stack()
{
tos = 0;
}
void stack::push(int x)
{
if(!is_full())
arr[tos++] = x;
else
cout « “Stack is full, Can not push " « x « endl;
}
int stack::pop()
{
if(!is_empty())
return arr[–tos];
else
cout « “Stack is empty, cannot pop” « endl;
return -1;
}
bool stack::is_empty()
{
if(tos == 0)
return true;
else
return false;
}
bool stack::is_full()
{
if(tos == STACKSIZE)
return true;
else
return false;
}
int stack::size()
{
return tos;
}
void stack::display()
{
if(tos == 0)
{
cout « “No elements to display” « endl;
return;
}
for(int i=0;i
cout « arr[i] « " “;
cout « endl;
}
int main()
{
stack mystack;
cout « mystack.size() « endl;
mystack.push(1);
if(mystack.is_full())
cout « “stack is full” « endl;
mystack.pop();
if(mystack.is_empty())
cout « “stack is empty” « endl;
}

  
Thanks.