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AccountAddrResolverI.sol

pragma solidity ^0.4.25;

contract AccountAddrResolverI {
    
    address public addr;
    
    address owner;
    
    function AccountAddrResolverI(){
        owner = msg.sender;
    }
    
    function changeOwner(address newowner){
        if (msg.sender != owner) throw;
        owner = newowner;
    }
    
    function getAddress() returns (address oaddr){
        return addr;
    }
    
    function setAddr(address newaddr){
        if (msg.sender != owner) throw;
        addr = newaddr;
    }
    
}

App.sol

pragma solidity ^0.4.25;

 import "./usingAccount.sol";

 contract App is usingAccount {

       uint public DieselPriceUSD;

       function App() {

                // OAR = AccountAddrResolverI(0x920cd3f7ed02c5d61e2556308d53a4d9d1e58bf2); 
       }

    

      function update(uint amount) payable {
          add(amount);
     }
     
     function getBalance(uint amount) public view returns (uint) {
          return get();
     }

}

usingAccount.sol

pragma solidity 0.4.25;

contract AccountI {
    
    address public cbAddress;
    
    function add(uint _amount) public returns (uint);
    function deduct(uint _amount) public returns (uint);
    function get() public view returns (uint);
    
}

contract AccountAddrResolverI {
    function getAddress() public returns (address _addr);
}

contract usingAccount {
    
    AccountAddrResolverI OAR;
    AccountI account;
    
    event LogAddress(address str);
    
    modifier accountAPI {
        OAR = AccountAddrResolverI(0x4a75E1bcB8a19Cf1bEe802BFA0F81df25Aa1510b);
        
        emit LogAddress(OAR.getAddress());
        
        if(address(account) != OAR.getAddress())
            account = AccountI(OAR.getAddress());
            
        _;
    }
    
    function add(uint _amount) public accountAPI returns (uint) {
        return account.add(_amount);
    }
    
    function deduct(uint _amount) public accountAPI returns (uint) {
        return account.deduct(_amount);
    }
    
    function get() public accountAPI returns (uint) {
        return 10;
    }
    
    function account_cbAddress() accountAPI internal returns (address){
        return account.cbAddress();
    }
    
/*    function __callback(bytes32 myid, string result) public {
        __callback(myid, result, new bytes(0));
    }
    function __callback(bytes32 myid, string result, bytes proof) public {
        return;
        // Following should never be reached with a preceding return, however
        // this is just a placeholder function, ideally meant to be defined in
        // child contract when proofs are used
        myid; result; proof; // Silence compiler warnings
        oraclize = OraclizeI(0); // Additional compiler silence about making function pure/view.
    }*/
}