dummy.c

#include <stdio.h>
#include <string.h>
#include <conio.h>

/* Global Declarations */
int pos = 0;
int top;
int length;
char symbol;
char temp;
char s[30];
char infix;
char prefix;

void push(char sym)
{
   top = top + 1;
   s[top] = sym;
}

char pop ()
{
  char item;
  item = s[top];
  top = top-1;
  return item;
}

int G (char symbol)
{
  switch (symbol)
  {
    case '+':
    case '-': return 2;
    case '*':
    case '/': return 4;
    case '^':
    case '$': return 5;
    case '(': return 0;
    case ')': return 9;
    default : return 7;
  }

}
int F (char symbol)
{
  switch (symbol)
  {
    case '+':
    case '-': return 1;
    case '*':
    case '/': return 3;
    case '^':
    case '$': return 6;
    case '(': return 0;
    case '#': return -1;
    default : return 8;
  }

}

void infix_prefix (char infix[], char prefix[])
{
  int i, t1;
  top = -1;
  length = strlen(infix);
  length = length - 1;
  pos = length;
  t1 = length;


while ( length >= 0)
{
   symbol = infix[length];
   switch(symbol)
   {

      case ')': push(symbol);
                break;

      case '(':
                temp = pop();
                while( temp != ')')
                {
                     prefix[pos] = temp;
                     pos--;
                     temp = pop();
                }
                if (temp != ')')
                {
                   prefix[pos--] = pop();
                }
                   break;
     case '+':
     case '-':
     case '*':
     case '$':
     case '/':
     case '^': while(F(s[top]) >= G(symbol))
               {
                 temp = pop();
                 prefix[pos] = temp;
                 pos--;
               }
                 push(symbol);
                 break;
     default:
                 prefix[pos--] = symbol;
                 break;
   }
    length--;
    {
          while(s[] != '#')
          {
             temp = pop();
             prefix[pos--] = temp;
          }
    for (i = 0; i < t1; i++)
    {
         prefix[i] = prefix[i + pos + 1];
    }
/* MAIN PROGRAM */
void main ()
{
 clrscr();
 printf("Enter the valid infix expression\n');
 scanf("%s",infix);
 infix_prefix(infix, prefix);
 printf("The prefix expression \n");
 printf("%s\n",prefix);
 getch();
}