postfix expression C++

[Shahbaz Ladak]

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;

}

/* SAMPLE OUTPUT:

Enter Postfix Exp<b></b>ression : 3 5 + 2 /

3 5 + 2 / EQUALS 4

*/


// End Code