S4- dsa lab - VALIDITY OF EXPRESSION

         /*              VALIDITY OF EXPRESSION       */

import java.io.*;

class Stack

{

int top=0;

char a[]=new char[100];

void push(char d)

{

top++;

a[top]=d;

}

char pop()

{

char d=a[top];

top--;

return d;

}

int em()

{ if(top==0)

return 1;

else return 0;

}}

class Expression

{

public static void main(String args[])throws Exception

{

DataInputStream nn=new DataInputStream(System.in);

System.out.print("enter the Expression: ");

String s=nn.readLine();

Stack ss=new Stack();

int n=s.length();

int flag=0,cc=0;

char d;

for(int i=0;i<n&&cc>=0;i++)

{

char c=s.charAt(i);

switch(c)

{

case '(' : ss.push('(');cc++;break;

case '{' : ss.push('{');cc++;break;

case '[' : ss.push('[');cc++;break;

case ')' : if((d=ss.pop())!='(')

               flag=1;cc--;break;

case '}' : if((d=ss.pop())!='{')

               flag=1;cc--;break;

case ']' : if((d=ss.pop())!='[')

               flag=1;cc--;break;

}

}

if((flag==0)&&(ss.em()==1))

{System.out.println("valid Expression ");

}

else

{System.out.println("invalid Expression ");

}}}

OUTPUT

enter the Expression: {a+(b*c)-d)

invalid Expression

enter the string  : {a+(b*c)-d}

valid Expression