Postfix Evaluation

$$$ POSTFIX EVALUATION $$$

PROGRAM:

#include<iostream>

#include<string.h>

int stack[20],top=-1;

int len,a,b,c,i,x;

char expr[20];

class postfix

{

      public:

      void evaluate()

      {

            len=strlen(expr);

            for(i=0;i<len;i++)

            {

                  if(expr[i]=='+'||expr[i]=='-'||expr[i]=='*'||expr[i]=='/')

                  {

                        b=pop();

                        a=pop();

                        switch(expr[i])

                        {

                              case '+':c=a+b;

                              push(c);

                              break;

                              case '-':c=a-b;

                              push(c);

                              break;

                              case '*':c=a*b;

                              push(c);

                              break;

                              case '/':c=a/b;

                              push(c);

                              break;

                        }

                  }

                  else

                  {

                        cout<<"Enter the value of"<<expr[i]<<":";

                        cin>>x;

                        push(x);

                  }

            }

      }

      void push(int item)

      {

            stack[++top]=item;

      }

      int pop()

      {

            int a;

            a=stack[top];

            top=top-1;

            return a;

      }

};

void main()

{

      postfix p;

      cout<<"$$$ POSTFIX EVALUATION $$$";

      cout<<"\nEnter the postfix expression:";

      cin>>expr;

      p.evaluate();

      cout<<"The resultant value is :"<<stack[top];

}

OUTPUT:

$$$ POSTFIX EVALUATION $$$

Enter the postfix expression: abc+*
Enter the value of a: 10
Enter the value of b: 20
Enter the value of c: 30
The resultant value is : 500