Program for Infix to Postfix Conversion

import java.io.*;
import java.io.DataInputStream;
class Stack
{
char items[]=new char[10];
int top;
Stack()
{
top=-1;
}
void push (char item)
{
if (top==9)
System.out.println("Stack overflow");
else
items[++top]=item;
}/*end push*/


int isempty()
{
if (top<0)
return 1;
else
return 0;
}/*end isempty*/
char pop()
{
if (isempty()==1)
{
System.out.println("Stack underflow");
return 0;
}
else
return (items[top--]);
}/*end pop*/
}/*end class stack*/
//-------------------------------------------------------------------------------------------------------------------
class Functions
{
void postfix(char infix[],char post[])
{
int position,und=1;
int outpos=0;
char topsymb='+';
char symb;
Stack opstk=new Stack();
opstk.top=-1;
for(position =0;(symb=infix[position])!='\0';position++)
{
if(isoperand(symb))
post[outpos++]=symb;
else
{
if (opstk.isempty()==1)
und=1;
else
{
und=0;
topsymb=opstk.pop();
}
while(und==0 && prcd(topsymb,symb)==1)
{
post[outpos++]=topsymb;
if (opstk.isempty()==1)
und=1;
else
{
und=0;
topsymb=opstk.pop();
}
}//end while
if(und==0)
opstk.push(topsymb);
if(und==1||(symb!=')'))
opstk.push(symb);
else
topsymb=opstk.pop();
}//end else
}//end for
while(opstk.isempty()==0)
post[outpos++]=opstk.pop();
post[outpos]='\0';
}//end postfix function
//-------------------------------------------------------------------------------------------------------------------
int prcd(char topsymb,char symb)
{
/*check precedence and return 0 or 1*/
if(topsymb=='(')
return 0;
if(symb=='(')
return 0;
if(symb==')')
return 1;
if (topsymb=='$'&&symb=='$')
return 0;
if (topsymb=='$'&&symb!='$')
return 1;
if (topsymb!='$'&&symb=='$')
return 0;
if((topsymb=='*'||topsymb=='/')&&(symb!='$'))
return 1;
if((topsymb== '+'||topsymb=='-')&&(symb=='-'||symb=='+'))
return 1;
if((topsymb== '+'||topsymb=='-')&&(symb=='*'||symb=='/'))
return 0;
return 1;
}/*end prcd function*/
//-------------------------------------------------------------------------------------------------------------------
boolean isoperand(char symb)
{
/*Return 1 if symbol is digit and 0 otherwise*/
if(symb>='0'&& symb<='9')
return true;
else
return false;
}/* end isoperand function*/
}
//-------------------------------------------------------------------------------------------------------------------
class InToPost
{
public static void main(String args[])
{
/*Read infix expression and call postfix function*/
Functions f=new Functions();
char infix[]=new char[80];
char post[]=new char[80];
int pos=0;char c;
DataInputStream in=new DataInputStream(System.in);
System.out.println("\nEnter an expression is infix form : ");
try
{
do
{
c=(char)in.read();
infix[pos++]=c;
}while(c!='\n');
}
catch(Exception e)
{
System.out.println("I/O Error");
}
infix[--pos]='\0';
System.out.println("The original infix expression is : ");
for (int i=0;i<pos;i++)
System.out.print(infix[i]);
f.postfix(infix,post);
System.out.println("\nThe postfix expression is : ");
for (int i=0;post[i]!='\0';i++)
System.out.println(post[i]);
}//end main
}


/*


Sample Input and Output :
Enter an expression is infix form : (1+2)*(3+4)
The Original infix expression is : (1+2)*(3+4)
The postfix expression is : 12+34+*


Enter an expression is infix form : 1$2*3-4+5/6/(7+8)
The original infix expression is : 1$2*3-4+5/6/(7+8)
The postfix expression is : 12$3*4-56/78+/+


Enter an expression is infix form : ((1+2)*3-(4-5))$(6+7)
The original infix expression is : ((1+2)*3-(4-5))$(6+7)
The postfix expression is : 12+3*45--67+$


Enter an expression is infix form : 1-2/(3*4$5)
The original infix expression is : 1-2/(3*4$5)
The postfix expression is : 12345$*/-


Enter an expression is infix form : ((1-(2+3))*4)$(5+6)
The original infix expression is : ((1-(2+3))*4)$(5+6)
The postfix expression is : 123+-4*56+$


*/