PROBLEM W/ EVALUATE....plz help me!
Code:
#include <stdio.h>
#include <ctype.h>
#define MAX 50
#define EMPTY -1
struct stack
{
int data[MAX];
int top;
};
int isempty(struct stack *s)
{
return (s->top == EMPTY) ? 1 : 0;
}
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 isoperator(char e)
{
if(e == '+' || e == '-' || e == '*' || e == '/' || e == '%')
return 1;
else
return 0;
}
int priority(char e)
{
int pri = 0;
if(e == '*' || e == '/' || e =='%')
pri = 2;
else
{
if(e == '+' || e == '-')
pri = 1;
}
return pri;
}
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 */
op2 = pop(&stk);
op1 = pop(&stk);
switch(*p)
{
case '+':
result = op1 + op2;
break;
case '-':
result = op1 - op2;
break;
case '/':
result = op1 / op2;
break;
case '*':
result = op1 * op2;
break;
case '%':
result = op1 % op2;
break;
default:
printf("\nInvalid Operator");
return 0;
}
push(&stk,result);
}
p++;
}
result = pop(&stk);
return result;
}
void infix2postfix(char* infix, char * postfix, int insertspace)
{
char *i,*p;
struct stack X;
char n1;
emptystack(&X);
i = &infix[0];
p = &postfix[0];
while(*i)
{
while(*i == ' ' || *i == '\t')
{
i++;
}
if( isdigit(*i) || isalpha(*i) )
{
while( isdigit(*i) || isalpha(*i))
{
*p = *i;
p++;
i++;
}
/*SPACE CODE*/
if(insertspace)
{
*p = ' ';
p++;
}
/*END SPACE CODE*/
}
if( *i == '(' )
{
push(&X,*i);
i++;
}
if( *i == ')')
{
n1 = pop(&X);
while( n1 != '(' )
{
*p = n1;
p++;
/*SPACE CODE*/
if(insertspace)
{
*p = ' ';
p++;
}
/*END SPACE CODE*/
n1 = pop(&X);
}
i++;
}
if( isoperator(*i) )
{
if(isempty(&X))
push(&X,*i);
else
{
n1 = pop(&X);
while(priority(n1) >= priority(*i))
{
*p = n1;
p++;
/*SPACE CODE*/
if(insertspace)
{
*p = ' ';
p++;
}
/*END SPACE CODE*/
n1 = pop(&X);
}
push(&X,n1);
push(&X,*i);
}
i++;
}
}
while(!isempty(&X))
{
n1 = pop(&X);
*p = n1;
p++;
/*SPACE CODE*/
if(insertspace)
{
*p = ' ';
p++;
}
/*END SPACE CODE*/
}
*p = '\0';
}
int main(void)
{
char infix[MAX], postfix[MAX], result[MAX];
printf("Enter expression: ");
fflush(stdin);
gets(infix);
infix2postfix(&infix[0],&postfix[0],1);
printf("\nPostfix expression is: %s",&postfix[0]);
result[0]=postfix[0];
printf("\n %s = %d.",&infix[0],evaluate(&result[0]));
return 0;
}
Re: PROBLEM W/ EVALUATE....plz help me!
I changed added two conditions in your code its working fine.
1. In the infix2postfix function while checking the operator pop function returns -1. so it adds that is also in stack. so after checking you can push that into the stack.
Code:
if( isoperator(*i) )
{
if(isempty(&X))
push(&X,*i);
else
{
n1 = pop(&X);
while(priority(n1) >= priority(*i))
{
*p = n1;
p++;
/*SPACE CODE*/
if(insertspace)
{
*p = ' ';
p++;
}
/*END SPACE CODE*/
n1 = pop(&X);
}
if(n1!=-1)
push(&X,n1);
push(&X,*i);
}
i++;
}
2. Then in the evaluate function after removing the spaces you need to check whether it is reached null or not.
Code:
while(*p != '\0')
{
/* removes tabs and spaces */
while(*p == ' ' || *p == '\t' )
{
p++;
}
if(*p == '\0')
break;
After changing these conditions try to execute it will work fine.
