Program to convert an Infix Expression into a Postfix Expression using Linked List as a Stack

 # include <iostream.h>
 # include   <string.h>
 # include   <stdlib.h>
 # include    <conio.h>

 struct node
 {
    char data;

    node *next;
 };

 node *top=NULL;
 node *bottom=NULL;
 node *entry;
 node *last_entry;
 node *second_last_entry;

 void push(const char);
 const char pop( );

 void infix_to_postfix(const char *);

 int main( )
    {
       clrscr( );

       char Infix_expression[100]={NULL};

       cout<<\"\\n\\n Enter the Infix Expression : \";
       cin>>Infix_expression;

       infix_to_postfix(Infix_expression);

       getch( );
       return 0;
    }


 //-----------------------------  push(const char)  ----------------------//


 void push(const char Symbol)
    {
       entry=new node;

       if(bottom==NULL)
      {
         entry->data=Symbol;
         entry->next=NULL;
         bottom=entry;
         top=entry;
      }

       else
      {
         entry->data=Symbol;
         entry->next=NULL;
         top->next=entry;
         top=entry;
      }
    }


 //--------------------------------  pop( )  -----------------------------//


 const char pop( )
    {
       char Symbol=NULL;

       if(bottom==NULL)
      cout<<\"\\n\\n\\n\\t ***  Error : Stack is empty. \\n\"<<endl;

       else
      {
         for(last_entry=bottom;last_entry->next!=NULL;
                         last_entry=last_entry->next)
        second_last_entry=last_entry;

         if(top==bottom)
        bottom=NULL;

         Symbol=top->data;

         delete top;

         top=second_last_entry;
         top->next=NULL;
      }

       return Symbol;
    }


 //---------------------  infix_to_postfix(const char *)  ----------------//


 void infix_to_postfix(const char *Infix)
    {
       char Infix_expression[100]={NULL};
       char Postfix_expression[100]={NULL};

       strcpy(Infix_expression,\"(\");
       strcat(Infix_expression,Infix);
       strcat(Infix_expression,\")\");

       char Symbol[5]={NULL};
       char Temp[5]={NULL};

       for(int count=0;count<strlen(Infix_expression);count++)
      {
         Symbol[0]=Infix_expression[count];

         if(Symbol[0]==\'(\')
        push(Symbol[0]);

         else if(Symbol[0]==\')\')
        {
           Symbol[0]=pop( );

           while(Symbol[0]!=\'(\')
              {
             strcat(Postfix_expression,Symbol);

             Symbol[0]=pop( );
              }
        }

         else if(Symbol[0]==\'^\' || Symbol[0]==\'*\' || Symbol[0]==\'/\'
                    || Symbol[0]==\'+\' || Symbol[0]==\'-\')
        {
           if(Symbol[0]==\'*\' || Symbol[0]==\'/\')
              {
             Temp[0]=pop( );

             while(Temp[0]==\'^\' || Temp[0]==\'*\' || Temp[0]==\'/\')
                {
                   strcat(Postfix_expression,Temp);

                   Temp[0]=pop( );
                }

             push(Temp[0]);
              }

           else if(Symbol[0]==\'+\' || Symbol[0]==\'-\')
              {
             Temp[0]=pop( );

             while(Temp[0]!=\'(\')
                {
                   strcat(Postfix_expression,Temp);

                   Temp[0]=pop( );
                }

             push(Temp[0]);
              }

           push(Symbol[0]);
        }

         else
        strcat(Postfix_expression,Symbol);
      }

       cout<<\"\\n\\n Postfix Expression : \"<<Postfix_expression;
    }