Java program for infix-postfix conversion

import java.util.*;

class Infix_Postfix

{

String infix;

char stack[];

int top; String postfix;

Infix_Postfix()

{

stack =new char[100];

top=-1;

}

public void get()

{

Scanner sc=new Scanner(System.in);

System.out.println("Enter the infix expression and keep a gap between the symbols");

infix=sc.nextLine();

}

public void Push(char ch)

{

if(top>=99)

{

System.out.println("Stack overflow");

return;

}

stack[++top]=ch;

}

public char pop()

{

if(top==-1)

{

System.out.println("Stack underflow");

return '@';

}

return stack[top--];

}

public int precedence(char ch)

{

switch(ch)

{

case '^':return 3;

case '*':

case '/':

case '%':return 2;

case '+':

case '-':return 1;

default:return 0;

}

}

public boolean isDigit(char ch)

{

if(ch>='0' && ch<='9')

return true;

return false;

}

public void convert()

{

get();

char ch;

infix=infix+" ) ";

Push('(');

String wd="";

postfix="";

System.out.println(infix);

for(int i=0;i<infix.length();i++)

{

if(isDigit(wd.charAt(0)))

postfix+=wd+" ";

else if(wd.charAt(0)=='(')

Push('(');

else if(stack[top]=='(')

{

while(true)

{

ch=pop();

if(ch=='(')

break;

postfix+=ch+" ";

}

wd="";

}

else

wd=wd+infix.charAt(i);

}

}

public void display()

{

System.out.println("The result is " + postfix);

}

}