How can I modify stored data in blockchain

Question

How can I alter a data stored in a block.  consider this code snippet,

{
    studentId:600,
    marks:300
}

Suppose, the above code was written to include a data entry in the blockchain. Now, I want to update this marks to 400. so can i do this in a block chain. I heard that we couldn't update a bockchain

Answer 1

One of the important feature of a blockchain is immutability, which means that any transaction once recorded cannot be altered. The only way to maodify is to add the updated data in a new a new blockchain.

So, instead of the code to change the marks from 400 to 500 you should add a new point of data to the variable. Also, if you want to reduce the marks, you have to add it in a new block and save it to the variable.