Crc.java

import java.util.Scanner;

public class Crc {
    static Scanner sc = new Scanner(System.in);
    
    static void readArray(int[] arr) {
        for (int i = 0; i < arr.length; i++) {
            arr[i] = sc.nextInt();
        }
    }
    
    static void calculateCrc(int[] generator, int[] remainder) {
        int current = 0;
        while (remainder.length - current >= generator.length) {
            for (int i = 0; i < generator.length; i++) {
                remainder[current + i] ^= generator[i];
            }
            
            while (remainder[current] == 0 && current != remainder.length - 1) {
                current++;
            }
        }
    }
    
    static boolean isValidCrc(int[] remainder) {
        for (int item : remainder) {
            if (item != 0) return false;
        }
        return true;
    }
    
    public static void main(String[] args) {
        System.out.print("Enter no of data bits: ");
        int[] dataWord = new int[sc.nextInt()];
        System.out.println("Enter data bits:");
        readArray(dataWord);
        
        System.out.print("Enter no of generator bits: ");
        int[] generator = new int[sc.nextInt()];
        System.out.println("Enter generator bits:");
        readArray(generator);
        
        int totalBits = dataWord.length + generator.length - 1;
        int[] codeWord = new int[totalBits];
        int[] remainder = new int[totalBits];
        
        System.arraycopy(dataWord, 0, codeWord, 0, dataWord.length);
        System.out.print("Dividend:");
        for (int item : codeWord) {
            System.out.print(" " + item);
        }
        System.out.println();
        
        System.arraycopy(codeWord, 0, remainder, 0, codeWord.length);
        computeCrc(generator, remainder);
        for (int i = 0; i < totalBits; i++) {
            codeWord[i] ^= remainder[i];
        }
        
        System.out.print("Transmitted code word:");
        for (int item : codeWord) {
            System.out.print(" " + item);
        }
        System.out.println();
        
        System.out.print("Enter a new code word:");
        readArray(codeWord);
        
        System.arraycopy(codeWord, 0, remainder, 0, codeWord.length);
        computeCrc(generator, remainder);
        if (isValidCrc(remainder)) {
            System.out.println("No error");
        } else {
            System.out.println("ERROR");
        }
    }
}