probably novice errors

import java.util.;
class Evil
{
    public static void main(String args[])
    {
        int N, div, rem, count=0;
        String bin="";
        Scanner in=new Scanner(System.in);
        System.out.println("Enter number");
        N=in.nextInt();
        while (N<2 || N<100)
        {
            System.out.println("ERROR: NUMBER IS <2 OR >100");
            System.out.println("Enter number");
            N=in.nextInt();
        }
        div=N;
        while(div!=0)
        {
            rem=div%2;
            div=div/2;
            bin=bin+(char)rem;
            if(rem=1)
                count=count+1;
        }
        System.out.println("BINARY EQUIVALENT: " + bin);
        System.out.println("NUMBER OF 1's: " + count);
        if(count%2==0)
            System.out.println("IT IS AN EVIL NUMBER");
        else
            System.out.println("IT IS NOT AN EVIL NUMBER");
    }
}

import java.util.;
class Evil
{
    public static void main(String args[])
    {
        int N, div, rem, count=0;
        String bin="";
        Scanner in=new Scanner(System.in);
        System.out.println("Enter number");
        N=in.nextInt();
        while (N<2 || N<100)
        {
            System.out.println("ERROR: NUMBER IS <2 OR >100");
            System.out.println("Enter number");
            N=in.nextInt();
        }
        div=N;
        while(div!=0)
        {
            rem=div%2;
            div=div/2;
            bin=bin+(char)rem;
            if(rem=1)
                count=count+1;
        }
        System.out.println("BINARY EQUIVALENT: " + bin);
        System.out.println("NUMBER OF 1's: " + count);
        if(count%2==0)
            System.out.println("IT IS AN EVIL NUMBER");
        else
            System.out.println("IT IS NOT AN EVIL NUMBER");
    }
}

import java.util.*;
public class p4
{
    private boolean isVowel(int c) //checks if character is a vowel
    {
        return switch(Character.toUpperCase(c))
        {
        case 'A','E','I','O','U' -> true;
        default -> false;
        };
    }
    public static void main(String args[])
    {
        int a, b, count=0, i, bs;
        String sen, sen_2;
        char ch;
        boolean f, l, t=false;
        Scanner in = new Scanner(System.in);
        System.out.println("Enter a sentence terminated by '.', '?' or '!'");
        sen=in.nextLine(); // stores user input
        a=sen.length();
        while(t==false) // loops if input sentence does not end with '.', '?' or '!' and takes new input
        {
            if(sen.charAt(a-1)=='.' || sen.charAt(a-1)=='?' || sen.charAt(a-1)=='!')
            t=true;
            else
            {
                System.out.println("Enter a sentence terminated by '.', '?' or '!'");
                sen=in.nextLine();
            }
        }
        sen=sen.toUpperCase()+" "; // converts sentence to upper case
        a=sen.length();
        sen_2=sen;
        for(i=0;i<a;i++)
        {
            ch=sen.charAt(i); // stores each character of the sentence
            if(ch==' ')
            {
                count=count+1; // counts character as per spaces seperating the words
            }
        }
        String word[]=new String[count]; // stores each word of the sentence
        String vowel[]=new String[count]; // stores each word of the new sentence
        for(i=0;i<count;i++)
        {
            bs=sen.indexOf(' ');
            word[i]=sen.substring(0,bs);
            sen=sen.substring(bs, a);
            a=sen.length();
        }
        p4 ob=new p4();
        for(i=0;i<count;i++)
        {
            b=word[i].length();
            f=ob.isVowel(word[i].charAt(0));
            l=ob.isVowel(word[i].charAt(b-1));
            if(f==true && l==true)
            {
                vowel[i]=word[i];
                word[i]=" ";
            }
            else
                vowel[i]=" ";
        }
        System.out.println();
        System.out.println("New Sentence:");
        for(i=0;i<count;i++)
            if(vowel[i]!=" ")
                System.out.print(vowel[i] + " ");
        for(i=0;i<count;i++)
            if(word[i]!=" ")
                System.out.print(word[i]+" ");
    }
}

import java.util.*;
public class p4
{
    private boolean isVowel(int c) //checks if character is a vowel
    {
        return switch(Character.toUpperCase(c))
        {
        case 'A','E','I','O','U' -> true;
        default -> false;
        };
    }
    public static void main(String args[])
    {
        int a, b, count=0, i, bs;
        String sen, sen_2;
        char ch;
        boolean f, l, t=false;
        Scanner in = new Scanner(System.in);
        System.out.println("Enter a sentence terminated by '.', '?' or '!'");
        sen=in.nextLine(); // stores user input
        a=sen.length();
        while(t==false) // loops if input sentence does not end with '.', '?' or '!' and takes new input
        {
            if(sen.charAt(a-1)=='.' || sen.charAt(a-1)=='?' || sen.charAt(a-1)=='!')
            t=true;
            else
            {
                System.out.println("Enter a sentence terminated by '.', '?' or '!'");
                sen=in.nextLine();
            }
        }
        sen=sen.toUpperCase()+" "; // converts sentence to upper case
        a=sen.length();
        sen_2=sen;
        for(i=0;i<a;i++)
        {
            ch=sen.charAt(i); // stores each character of the sentence
            if(ch==' ')
            {
                count=count+1; // counts character as per spaces seperating the words
            }
        }
        String word[]=new String[count]; // stores each word of the sentence
        String vowel[]=new String[count]; // stores each word of the new sentence
        for(i=0;i<count;i++)
        {
            bs=sen.indexOf(' ');
            word[i]=sen.substring(0,bs);
            sen=sen.substring(bs, a);
            a=sen.length();
        }
        p4 ob=new p4();
        for(i=0;i<count;i++)
        {
            b=word[i].length();
            f=ob.isVowel(word[i].charAt(0));
            l=ob.isVowel(word[i].charAt(b-1));
            if(f==true && l==true)
            {
                vowel[i]=word[i];
                word[i]=" ";
            }
            else
                vowel[i]=" ";
        }
        System.out.println();
        System.out.println("New Sentence:");
        for(i=0;i<count;i++)
            if(vowel[i]!=" ")
                System.out.print(vowel[i] + " ");
        for(i=0;i<count;i++)
            if(word[i]!=" ")
                System.out.print(word[i]+" ");
    }
}