Stack push pop
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A stack is a linear data structure that follows the LIFO (last in, first out) principle. Elements are added to the top of the stack and removed from the top. A pointer called the top pointer tracks the top element of the stack during push and pop operations. The push operation adds an element to the top of the stack, while the pop operation removes the top element. A stack can be implemented using either an array or linked list. The document then provides algorithms and sample code for implementing stack operations like push and pop on an array-based stack.
![6
5
4 D
3 Q
2 F
1 A
(a) Before push
(b) After push
Fig. 2: Pictorial view of push operation
Algorithm to add an element to a stack
1. Declare the stack and top:
stack[[1…..M], top;
2, Add an item in the stack:
if(top<M)
{
top=top+1;
stack[top]=item;
}
else print “Over Flow”;
3. Output will be the updated stack.
Pop Operation
Pop operation means to delete (access) an element from a stack. Here, top is an indicator indicates
the top element of the stack, M is the size of the array and x is a variable where we access top
element of the stack.
6
5
4 D
3 Q
2 F
1 A
(a) Before pop (b) After pop
Fig. 3: Pictorial view of pop operation
6
5 H
4 D
3 Q
2 F
1 A
6
5 H
4 D
3 Q
2 F
1 A
top
(top=4
)
top
(top=5
)
top
(top=5
)
top
(top=4
)](https://image.slidesharecdn.com/stackpushpop-210706150904/85/Stack-push-pop-2-320.jpg)
![Algorithm to delete an element from a stack
1. Declare the stack and top:
stack[1…..M], top;
2. Access the top element:
if (top==0) print “stack is empty”;
else {
x=stack[top];
top=top-1;
}
3. Output: updated list.
Sample Code
#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
void show(int stack[],int p)
{
printf("nThe stack is:n");
for(int j=1;j<=p;j++)
printf("%d ",stack[j]);
printf("n");
}
int main()
{
int i=0,n,a[50];
printf("Enter maximum size of stack:n");
scanf("%d",&n);
printf("n1.Pushn2.Popn3.Exitn");
while(1)](https://image.slidesharecdn.com/stackpushpop-210706150904/85/Stack-push-pop-3-320.jpg)
![{
printf("Enter your choice: ");
switch(getche())
{
case '1':if(i<n)
{
printf("nEnter element:");
i++;
scanf("%d",&a[i]);
show(a,i);
}
else
printf("nThe stack is
overflow.n");
break;
case '2':if(i>0)
{i--;
show(a,i);}
else
printf("nThe stack is
underflow.n");
break;
case '3': exit(0);
default: printf("nInvalid Selection.n") ;
break;
}
}
}](https://image.slidesharecdn.com/stackpushpop-210706150904/85/Stack-push-pop-4-320.jpg)
Stack push pop
- 1. Stack Stack is a linear list where any element is added at the top of the list and any element is deleted (accessed) from the top of the list. So, for stack an indicator or pointer must be used to indicate or point the top element of the stack. Add operation for a stack is called “push” operation and deletion operation is called “pop” operation. Stack is a LIFO (Last In First Out) structure. That means the element which was added last will be deleted or accessed first. The elements of a stack are added from bottom to top, means push operation is performed from bottom to top. The elements are deleted from top to bottom, which means pop operation is performed from top to bottom. Stack can be implemented using two ways; using array and using linked list. 8 7 6 5 1923 4 1452 3 2315 2 1245 1 1025 (a) Array based stack 40 48 59 67 63 (b) A link based stack Fig. 1: Graphical representation of stack Array Based Stack The stack, which is implemented using array is called array based stack. To create an array based stack, at first we have to declare an array with required size. Push Operation Push operation means to add an element to a stack. Here, we shall use array based stack. So, an array will be treated as a stack. We need an indicator or index identifier to add element to the stack and this indicator will mark the top of the stack. To add an element we have to check whether the array is already full or not. If the array is already full then we cannot add any element, otherwise we can. Here, top is an indicator indicates the top element of the stack and item is an element to be added to the stack, M is the size of the stack (array). Overflow occurs when we try to insert an element into the stack, which is already full. top (top=5 )
- 2. 6 5 4 D 3 Q 2 F 1 A (a) Before push (b) After push Fig. 2: Pictorial view of push operation Algorithm to add an element to a stack 1. Declare the stack and top: stack[[1…..M], top; 2, Add an item in the stack: if(top<M) { top=top+1; stack[top]=item; } else print “Over Flow”; 3. Output will be the updated stack. Pop Operation Pop operation means to delete (access) an element from a stack. Here, top is an indicator indicates the top element of the stack, M is the size of the array and x is a variable where we access top element of the stack. 6 5 4 D 3 Q 2 F 1 A (a) Before pop (b) After pop Fig. 3: Pictorial view of pop operation 6 5 H 4 D 3 Q 2 F 1 A 6 5 H 4 D 3 Q 2 F 1 A top (top=4 ) top (top=5 ) top (top=5 ) top (top=4 )
- 3. Algorithm to delete an element from a stack 1. Declare the stack and top: stack[1…..M], top; 2. Access the top element: if (top==0) print “stack is empty”; else { x=stack[top]; top=top-1; } 3. Output: updated list. Sample Code #include<stdio.h> #include<conio.h> #include<stdlib.h> void show(int stack[],int p) { printf("nThe stack is:n"); for(int j=1;j<=p;j++) printf("%d ",stack[j]); printf("n"); } int main() { int i=0,n,a[50]; printf("Enter maximum size of stack:n"); scanf("%d",&n); printf("n1.Pushn2.Popn3.Exitn"); while(1)
- 4. { printf("Enter your choice: "); switch(getche()) { case '1':if(i<n) { printf("nEnter element:"); i++; scanf("%d",&a[i]); show(a,i); } else printf("nThe stack is overflow.n"); break; case '2':if(i>0) {i--; show(a,i);} else printf("nThe stack is underflow.n"); break; case '3': exit(0); default: printf("nInvalid Selection.n") ; break; } } }
- 5. Sample Output Case 1 Enter maximum size of stack: 3 1.Push 2.Pop 3.Exit Enter your choice: 1 Enter element:5 The stack is: 5 Enter your choice: 1 Enter element:6 The stack is: 5 6 Enter your choice: 1 Enter element:7 The stack is: 5 6 7 Enter your choice: 1 The stack is overflow. Enter your choice: 3
- 6. Case 2: Enter maximum size of stack: 3 1.Push 2.Pop 3.Exit Enter your choice: 2 The stack is underflow. Enter your choice: 1 Enter element:2 The stack is: 2 Enter your choice: 1 Enter element:5 The stack is: 2 5 Enter your choice: 1 Enter element:8 The stack is: 2 5 8 Enter your choice: 1 The stack is overflow. Enter your choice: 2 The stack is:
- 7. 2 5 Enter your choice: 2 The stack is: 2 Enter your choice: 2 The stack is: Enter your choice: 2 The stack is underflow. Enter your choice: 3