INTOPRE.BAK

#include<stdio.h>
#include<conio.h>
#include<string.h>
#define max 20
char stack[max];
int top=-1;

void push(char x)
{
  if(top==(max-1))
     printf("overflow of stack");
  else
     stack[++top]=x;
}
char pop()
{
  if(top==-1)
  { printf("underflow of stack");
    return -1 ;
    }

  else
    {
      return(stack[top--]);
    }
}
int priority(char x)
{
   if(x=='(') return 0;
   else if(x=='+'|| x=='-') return 1;
   else if(x=='*'|| x=='/') return 2;
   else return -1;
}
void main()
{ int i,l,t1,t2,k=0;
  char exp[20],rev[20];
  clrscr();
  printf("Enter the infix expression\n");
  scanf("%s",exp);
  l=strlen(exp);
  for(i=l-1;i>=0;i--)
  { if(exp[i]=='(')
      rev[k++]=')';
    else if(exp[i]==')')
      rev[k++]='(';
      else
     rev[k++]=exp[i];
   }
   rev[k++]='\0';

  rev[k]=')';
  push('(');
  k=0;
  for(i=0;i<=l;i++)
  {
    if( (rev[i] >=97 && rev[i]<122) ||(rev[i] >=65 && rev[i]<90))
      {
       exp[k++]=rev[i];
      }
    else if(rev[i]=='(')
       push(rev[i]);
    else if(rev[i]==')')
      { while(stack[top]!='(')
	  exp[k++]=pop();
	pop();

      }
    else
    {  t1=priority(stack[top]);
       t2=priority(exp[i]);
      while(t1>t2 && stack[top]!='(')
	exp[k++]=pop();
      push(rev[i]);
   }
  }
 for(i=k-1;i>=0;i--)
  printf("%c",exp[i]);
  getch();
}