# Swap top two element of stack by R4R Team

What is Stack ?
Stack is a linear data structure which follows a particular order in which the operations are performed.
The order may be LIFO(Last In First Out) or FILO(First In Last Out).

How swap two two element :
Function:

void swap()
{
int temp;
temp=top->data;
top->data=top->back->top;
top->back->data=temp;
}

program-

#include< stdio.h>
#include< conio.h>
#include< alloc.h>
struct stack
{
int data;
struct stack *back;
};
struct stack *top;

void create()
{
char ch;
struct stack *ptr,*cpt;
printf("Enter Number\n");
cpt=(struct node*)malloc(sizeof(struct stack));
scanf("%d",&cpt->data);
cpt->back=NULL;
do
{
printf("Enter Number\n");
ptr=(struct stack*)malloc(sizeof(struct stack));
scanf("%d",&ptr->data);
ptr->back=cpt;
cpt=ptr;
printf("Continue(y/n)?n");
ch=getch();
}while(ch=='y');
top=cpt;
}

void traverse()
{
struct stack *ptr=top;
printf("Stack is :\n");
while(ptr!=NULL)
{
printf("%d ",ptr->data);
ptr=ptr->back;
}
}

void swap()
{
int temp;
temp=top->data;
top->data=top->back->top;
top->back->data=temp;
}

void main()
{
clrscr();
create();
traverse();
swap();
printf("After Swap Top Two element\n");
traverse();
getch();
}

output-

Enter Number
3
Enter Number
4
Continue(y/n)?
Enter Number
7
Continue(y/n)?
Enter Number
1
Continue(y/n)?
Stack is :
1 7 4 3
After Swap Top Two element
Stack is :
7 1 4 3