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In the first scenario, each time you call B.get(), you will deploy a new instance of A. If you call it 10 times, there will be 1 B contract, and 10 A contracts. In the second scenario, contract A is …

You do not have a payable function in your contract (besides the constructor, but that cannot be invoked after deployment). Try adding a payable fallback: function() public payable { } Then, send …

To my knowledge, no such service exists, although building one would not be terribly difficult if you have access to a node. Naturally, entrusting private keys to a third party is a terrible idea and …

It is likely failing during the deployment in the execution of your constructor. Within the constructor, you call: createCredential("A", "Associate Degree in Basket Weaving", "BA - Arts"); This en …

solc will generate the ABI for you (as will remix and truffle) Just run solc --abi yourfile.sol. You can see a list of compiler options here.

You are correct in the two scenarios depending on the order of execution. This is known as a front running attack, and many ERC20 token's approve functions are vulnerable to it: https://blog.smartdec. …

So, I am converting the data first to pdf and then creating the hash of pdf using Keccack 256 algorithm and storing the hash to the contract Why not just take the mongodb document output (JSON) a …

The contract is being created. The geth debug trace shows the CREATE opcode and storing of the code. Additionally, if you call getCode on geth for one of the deployed addresses (from this tx's log), …

You can't. Metamask follows a 1 dialog, 1 signature system for users' security. If you want to perform actions like this, you will need to implement your own signed (web3 has direct support for it), a …

Your code requires that the msg.value equals the amount parameter. Yet, your remix screenshot shows you are sending a 0 value tx with an amount of 10 as the parameter. This fails the require statemen …

Gas is not a currency. It is a unit of work. Gas is calculated based on the exact operations performed during the execution of a transaction. For smart contracts, this means it is based on what code …

Transactions are included in a block in a specific order. In your example, even if both transactions are in the same block, one will come before the other. In this case, the first tx in the block's t …

You're mixing two different parts here. When you look at etherscan's token page, you see the Transfer events emitted by the quantstamp contract. These are the events that log user to user transaction …

Yes, you can do this via the fallback function. If a contract is called with empty input data, or with a function signature that doesn't match any function on the contract, the fallback function is e …

Whether the contract is stalled or not depends on your exact implementation. If you have some function in your contract which iterates over the entire array every time it is called, then the contract …