Infix to postfix conversion

[zeroeight]

Hi guys,

I'm a newbie here, I just want to seek for help regarding my program. I want to implement an infix to postfix conversion only accepting numbers. Right now, I already debugged the errors and encountering loop everytime I execute it.

Here's my sample code:

************************************************** ******************

#include<stdio.h>
#include<conio.h>
#include<ctype.h>
 
 
struct stack_elem
{
 char elem[10];
 int topelem;
} stckmain;
 
void intoposconvert(char *infix, char *postfix, struct stack_elem *st)
{
 char *inf, *pos;
 struct stack_elem *s;
 char temp;
 int tctr;
 inf = &infix[0];
 pos = &postfix[0];
 s = st;
 
while(*inf){
 if ( *inf == '(' )
  {
   tctr=++s->topelem; /* increment the topelem */
   s->elem[tctr]=*inf; /*push*/
   temp=s->elem[tctr]; /*assign value pushed in stack in temp*/
   inf++;
  }
 else if ( *inf == ')' )
  {
   while ( temp != '(' )
    {
     tctr=s->topelem; /*assign top in tmp*/
     temp=s->elem[tctr]; /*assign value to be popped in temp*/
     --s->topelem; /*pop*/
     *pos=temp;
     pos++;
     inf++;
    }
  }
 else if (*inf == '*' || *inf == '/') /*data coming from ICP*/
  {
   if( s->topelem == -1 || s->elem[tctr] == '(' ) /*if stack is empty or entity in stack is '('*/
    {
     tctr=++s->topelem;
     s->elem[tctr]=*inf;
     temp=s->elem[tctr];
     inf++;
    }
   else /*else stack is not empty*/
    {
     temp=s->elem[tctr];
      if(temp == '+' || temp == '-')
       {
        tctr=++s->topelem;
    s->elem[tctr]=*inf;
    inf++;
       }
      else if (temp == '^')
       {
        tctr=s->topelem;
    temp=s->elem[tctr];
        --s->topelem;
        *pos=temp;
    pos++;
    inf++;
       }
      else if (temp == '*' || temp == '/')
      {
       tctr=s->topelem;
       temp=s->elem[tctr];
       --s->topelem;
       *pos=temp;
       pos++;
       inf++;
       tctr=++s->topelem;
       s->elem[tctr]=*inf;
      }
     }
   }
 else if (*inf == '+' || *inf == '-')
  {
   if( s->topelem == -1 || s->elem[tctr] == '(' ) /*if stack is empty or entity in stack is '('*/
    {
      tctr=++s->topelem;
      s->elem[tctr]=*inf;
      temp=s->elem[tctr];
      inf++;
    }
   else
    {
      temp=s->elem[tctr];
       if(temp == '*' || temp == '/' || temp == '^')
        {
          tctr=s->topelem;
      temp=s->elem[tctr];
          --s->topelem;
      *pos=temp;
      pos++;
      inf++;
        }
       else if(temp == '+' || temp == '-')
       {
     tctr=s->topelem;
     temp=s->elem[tctr];
     --s->topelem;
     *pos=temp;
     pos++;
     inf++;
     tctr=++s->topelem;
     s->elem[tctr]=*inf;
       }
     }
   }
 else if( isdigit(*inf) != 0)
  {
     temp=*inf;
     *pos=temp;
     pos++;
     inf++;
  }
 else
   printf("\n Not a valid input.");
 }
}
 
main()
{
 
char infix[50], postfix[50];
struct stack_elem *st;
 
clrscr();
st = &stckmain;
strcpy(stckmain.topelem, -1);
strcpy(stckmain.elem[0], "");
 
printf("Enter infix statement: ");
/*scanf("%d",&infix[0]);*/
fflush(stdin);
gets(infix);
intoposconvert(&infix[0], &postfix[0], st);
printf("\n Result in postfix statement: ");
printf("%s", postfix);
getch();
 
}
 

************************************************** *********************

Thanks!
-AR

[newb16]

I already debugged the errors and encountering loop everytime I execute it.

How can you execute it if it doesn't even compile? ( no, i'm not talking about conio.h includes that are not everywhere, I'm talking about strcpy)

[newb16]

if you change that line to
stckmain.topelem = -1;
it runs, but inserts open parenthesis where it shouldn't be.