Convert infix expression to postfix expression using stack in cpp[ c++ program] and using class.

 INFIX TO POSTFIX

 A+B*C+D-->>ABC*+D+

 ALGORITHM FOR INFIX TO POSTFIX CONVERSION:

1. Create an empty stack and an empty postfix output string/stream.
2. Scan the infix input string/stream left to right.
3. If the current input taken is an operand simply append it to the output string.
4. If the current taken is an operator,pop off all operators that have equal or higher precedence and append them to the output string . The order of popping is the order in the output.
5. If the current input token is " ( " push it into the stack.
6. If the current input token is " ) " pop off all operators and append them to string until a " ( "is popped discard the " (" .
7. If the end of input string is found ,pop all operators  and append them to the output string.  

PROGRAM FOR INFIX TO POSTFIX CONVERSION IN CPP:

#include<iostream.h>
#include<conio.h>
#include<ctype.h>

 struct node               //STRUCTURE
{
 char data;                  //DATA PART
 struct node *next;         //NEXT IS A POINTER POINTING TO NEXT NODE
}*top = NULL;

int prece(char token);

class stack                  //CLASS WITH NAME STACK
{
  public:

          void push(char x)       //INPUT DATA INTO NODE\STACK
     {
       struct node *p;
       p=new node;
       p->data=x;
       p->next=top;
       top=p;
     }
         char pop()            //REMOVE DATA FROM STACK
           {
      char x;
      x=top->data;
      top=top->next;
      return x;
           }
         void display()            //DISPLAY TOTAL NO DATA VALUE IN STACK NODE
           {
       struct node *p;
       p=top;
       while(p!=NULL)
         {
            cout<<"\n"<<p->data <<"\n";
            p=p->next;
         }
           }

char infix_postfix(char postfix[30],char infix[30]);

char top1()
 {
    return top->data;
 }

int empty()      //TO CHECK STACK IS EMPTY OR NOT
{
  if(top==NULL)
   return 1;
  else
   return 0;
}
};

char stack::infix_postfix(char postfix[30],char infix[30])
  {
    char token;
    int j=0;
    stack s;
      for(int i=0;infix[i]!='\0';i++)
       {
  token=infix[i];
    if(isalnum(token))     // CHECK OPERAND IS PRESENT OR NOT IF PRESENT ADD INTO POSTFIX ARRAY
    {
        postfix[j++]=token;
    }
    else if(token=='(')
    {
        s.push(token);
    }
    else if(token==')')
    {
       while(s.top1()!='(')
          {   
             postfix[j++]=s.pop();
          }
         s.pop();
    }
   else
    {
       while(prece(token)<=prece(s.top1()) && !s.empty())   //BEFORE INSERTING OPERATOR INTO STACK FIRST CHECK PRECEDENCE OF OPERATOR 
       {                                             //AND CHECK STACK IS EMPTY OR WHAT
         postfix[j++]=s.pop();
       }
      s.push(token);                                //PUSH OPERATOR INTO STACK
          }
   }
     while(s.top1()!=NULL)
      {
 postfix[j++]=s.pop();
       }
 postfix[j]='\0';
    return *postfix;
}


int prece(char token)                //PRECEDENCE FUNCTION TO CHECK PRECEDENCE OF OPERATOR
 {
   if(token=='*'||token=='/')
    return 3;
   else if(token=='+'||token=='-')
    return 2;
   else
    return 0;
 }


void main()
{
   stack s1;                                //CREATE OBJECT OF CLASS STACK
   char infix[30]={0},postfix[30]={0};
   
    cout<<"Enter infix Expression\n";
    cin>>infix;
    s1.infix_postfix(postfix,infix);                   // CALL INFIX_POSTFIX FUNCTION USING OBJECT
    cout<<postfix;
}

OUTPUT:

//****************OUTPUT*******************

Enter infix Expression
(A+B)
AB+