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Thread: can't create checksum algorithm/ can't understand concept of checksum

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    Talking can't create checksum algorithm/ can't understand concept of checksum

    Here is my code:

     
    int[] a = {1, 2, 3, 4, 5}
    checksum = 0;
    int i = 0;
     
    while ( a[i] < a.length-1  )
    {
      checksum += a[i] + a[i - 1] ;
      i++;
    }
     
    checksum %= i;

    Another problem is I can't really grasp what a "checksum" is. I've looked it up but don't get it. Could I have a simple example please? I need to fix my code ASAP.


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    Default Re: can't create checksum algorithm/ can't understand concept of checksum

    There are many different ways to implement a checksum. See: Wikipedia: List of Checksums.

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    Default Re: can't create checksum algorithm/ can't understand concept of checksum

    An implementation of a checksum varies, however its goal is always the same: To determine if data has been transported without errors or not.
    To show the the basic idea of a checksum, i've written a simple example which uses a very basic "summation" checksum, which computes the checksum based on the sum of all the payload bytes. Via the comments, assume this data array is transferred across a socket or whatever.

    	public static void main(String[] args){
     
    		//SENDER
    		final byte[] data = new byte[4];
    		data[0] = 1;
    		data[1] = 2;
    		data[2] = 3;
     
    		//calculate checksum
    		for(int i = 0; i < data.length-1; i++){
    			data[data.length-1] += data[i];
    		}
     
    		//RECEIVER
     
    		final byte[] received = data;
     
    		//calculate checksum
    		byte checksum = 0;
    		for(int i = 0; i < data.length-1; i++){
    			checksum += received[i];
    		}
     
    		//CHECKSUM DOESNT MATCH! DATA CORRUPTED!
    		if(checksum != received[4]){
    			System.out.println("An error occured");
    		}
     
    	}
    Please use [highlight=Java]//code goes here...[/highlight] tags when posting your code

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