Multiple smart contracts

Question

What is the process called when using e.g a token smart contract in an ICO smart contract? and could someone provide an explanation of the process. I'm not sure that I understand how interaction between multiple contracts works. Thank you very much.

Answer 1

In order to interact with other contract from your own, you need to have some sort of interface, for example interface for standard ERC20 token would look something like this:

contract ERC20_Token{
      function balanceOf(address _owner) constant returns (uint256 balance);
      function transfer(address _to, uint256 _value) returns (bool success);
      function transferFrom(address _from, address _to, uint256 _value) returns (bool success);
      function approve(address _spender, uint256 _value) returns (bool success);
      function allowance(address _owner, address _spender) constant returns (uint256 remaining);
      event Transfer(address indexed _from, address indexed _to, uint256 _value);
      event Approval(address indexed _owner, address indexed _spender, uint256 _value);
      uint public decimals;
      string public name;
}

Then you can call functions on other contract using this interface, you just need to provide address of contract that you are planning to use.

For example:

ERC20_Token("address of token contract").transfer("address","value");

Basically you can map all functions you want to use in the interface contract, for example if you just want to use transfer function you don't need to include all ERC20 standard functions. Note that your request will be coming from your contract and not your address you called contract from, so to transfer tokens you would need that token to be available on your contract address.