Thread: Postfix expression C++

I made a program and I have a problem here.

Problems ::
1. This code accepts 1 digit only if you enter 5 6 + this program shows 11 but it you enter 11 22 + it shows 4. please help me out to change it upto 3 digits.

2. If a user enters 2 operators like 30 40 + * it should display an error "Two operators are not allowed"

3. if user enters 6 2 3 + - 3 8 2 / + * 2 ^ 3 + result 52 should appear.

here is the code.....

Code:

 


#include <stdio.h>
#include <ctype.h>


#include <iostream>
#include <stdlib.h>
#include <string>
#include <sstream>
#include <fstream>
#include <cstdio>
#include <iomanip>
#include <cstdlib>


#define MAX 50
#define EMPTY -1




struct stack
{
    int data[MAX];
    int top;
};
 
void emptystack(struct stack* s)
{
    s->top = EMPTY;
}
void push(struct stack* s,int item)
{
    if(s->top == (MAX-1))
    {
        printf("\nSTACK FULL");
    }
    else
    {
        ++s->top;
        s->data[s->top]=item;
    }
}
 
int pop(struct stack* s)
{
    int ret=EMPTY;
    if(s->top == EMPTY)
        printf("\nSTACK EMPTY");
    else
    {
        ret= s->data[s->top];
        --s->top;
    }
    return ret;
}
void display(struct stack s)
{


    while(s.top != EMPTY)


    {


        printf("\n%d",s.data[s.top]);


        s.top--;


    }


}


 


int evaluate(char *postfix)


{


    char *p;


    struct stack stk;


    int op1,op2,result;


 


    emptystack(&stk);


    p = &postfix[0];


 


    while(*p != '\0')


    {


       /* removes tabs and spaces */


        while(*p == ' ' || *p == '\t')


        {


            p++;


        }


      /* if is digit */


        if(isdigit(*p))


        {


            push(&stk,*p - 48);


        }


        else


        {


           /* it is an operator */


            op1 = pop(&stk);


            op2 = pop(&stk);


 


            switch(*p)


            {


                case '+':
                    result = op2 + op1;
                    break;
                case '-':


                    result = op2 - op1;
                    break;


                case '/':


                    result = op2 / op1;
                    break;
                case '*':


                    result = op2 * op1;
                    break;


                case '%':


                    result = op2 % op1;
                    break;
                    
                case '^':


                    result = op2 ^ op1;
                    break;


                default:


                    printf("\nInvalid Operator");


                    return 0;


            }


            push(&stk,result);


        }


        p++;


    }


    result = pop(&stk);


    return result;


}


 


int main()


{


    char exp[MAX];


    printf("Enter Postfix Exp<b></b>ression : ");


    gets(exp);
    


    printf("%s EQUALS %d\n",exp,evaluate(&exp[0]));
    
    gets(exp); 
    return 0;


}

Can you give some general idea what this program is for?
Some examples? (there are some but the line is messed up so i didn't understand what you meant).