Tuesday, 29 March 2011

Infix to Postfix Conversion

Following is the java code for converting from infix to postfix:

// To convert Infix into Postfix

import java.io.*;

class infix2
{
 public static void main(String args[]) throws IOException
  {
    check obj=new check();
    String str = new String();
    char infix[]=new char[15];
    char postfix[]=new char[15];
    char stack[]=new char[15];
    int len=0,i=0,j=0,top=-1,value;
    BufferedReader b=new BufferedReader(new InputStreamReader(System.in));
    System.out.println("Enter Expression ==>  ");
    str=b.readLine();
    len=str.length();
    infix=str.toCharArray();
    for(i=0;i<=len-1;i++)
     {
      int t=obj.isoperand(infix[i]);
      if(t==1)
       {
         postfix[j]=infix[i];
         j++;
       }
      else
        if(top==-1)
          {
            top++;
	    stack[top]=infix[i];
 	  }
	else            
 	  if(infix[i]==')')
	    {
	      while(stack[top]!='(')
 	       {
                 postfix[j]=stack[top];
     	         top--;
	         j++;
	       }
              top--;
            }
          else
             if(obj.priority(infix[i])>obj.priority(stack[top]))
              {
	        top++;
	        stack[top]=infix[i];
              }
             else
              {
	        if(obj.priority(infix[i])==obj.priority(stack[top]))
                 {
                   postfix[j]=stack[top];
         	   top--;
	           j++;

                 }
               else
                 {
                  while(obj.priority(infix[i])<obj.priority(stack[top]) && top!=-1 && stack[top]!='(')
                   {
	           postfix[j]=stack[top];
         	   top--;
	           j++;
                  }
                 }
               top++;
               stack[top]=infix[i];
             }
          
     } //end of for loop
    while(top!=-1)
     {
       postfix[j]=stack[top];
       top--;
       j++;
     }
     System.out.println("The Postfix Expression is");
     for(i=0;i<len;i++)
      System.out.print(postfix[i]);
  }//end of main
}//end of class

class check
{
  int isoperand(char ch)
   {
     if((ch>='A' && ch<='Z' )|| (ch>='a' && ch<='z'))
        return 1;
     else
        return 0;
   }//end of isoperand method
	
  int priority(char ch)
   {
      if(ch=='(')
         return 4;
      if(ch=='^' || ch=='%')
         return 3;
      if(ch=='*' || ch=='/')
         return 2;
      if(ch=='+' || ch=='-') 
         return 1;
      if(ch==')')
         return 0;
      return -1;
   }//end of priority method
}//end of class check