# Gas requirement of a function is unknow

I wrote my own contract. Here it is:

``````  pragma solidity ^0.4.4;
contract SafeMath{
function safeMul(uint a, uint b) internal pure returns (uint) {
uint c = a * b;
assert(a == 0 || c / a == b);
return c;
}

function safeDiv(uint a, uint b) internal pure returns (uint) {
assert(b > 0);
uint c = a / b;
assert(a == b * c + a % b);
return c;
}

function safeSub(uint a, uint b) internal pure returns (uint) {
assert(b <= a);
return a - b;
}

function safeAdd(uint a, uint b) internal pure returns (uint) {
uint c = a + b;
assert(c >= a);
return c;
}

}

contract ERC20{

uint256 public totalSupply;
function balanceOf(address who) public view returns (uint256);
function transfer(address to, uint256 value) public returns (bool);

function approve(address spender, uint256 value) public returns (bool);

}

contract TestIco is ERC20, SafeMath{

uint256 public totalSupply;

function balanceOf(address _owner) public constant returns (uint256 balance) {
return balances[_owner];
}

function transfer(address _to, uint256 _value) public returns (bool success){
balances[msg.sender] = safeSub(balances[msg.sender], _value);
Transfer(msg.sender, _to, _value);
return true;
}

var _allowance = allowed[_from][msg.sender];

balances[_from] = safeSub(balances[_from], _value);
allowed[_from][msg.sender] = safeSub(_allowance, _value);
Transfer(_from, _to, _value);
return true;
}

function approve(address _spender, uint256 _value) public returns (bool success) {
allowed[msg.sender][_spender] = _value;
Approval(msg.sender, _spender, _value);
return true;
}

return allowed[_owner][_spender];
}

uint256 public endTime;

modifier during_offering_time(){
require(now <= endTime);
_;
}

function () public payable during_offering_time {
createTokens(msg.sender);
}

function createTokens(address recipient) public payable {
require(msg.value != 0);

uint tokens = safeDiv(safeMul(msg.value, price), 1 ether);

//require(owner.send(msg.value));
}

string  public name = "TestIco";
string  public symbol = "SCO";
uint    public decimals = 3;
uint256 public INITIAL_SUPPLY = 10000;
uint256 public price;

function TestIco() public {
totalSupply = INITIAL_SUPPLY;
balances[msg.sender] = INITIAL_SUPPLY;  // Give all of the initial tokens to the contract deployer.
endTime = now + 1 weeks;
owner   = msg.sender;
price   = 500;
}

}
``````

I use Remix to test the code. The problem is that it always give me 3 constant warning:

1. use of "now": "now" does not mean current time.

2. Fallback function of contract requires too much gas ().

3. Gas requirement of function INITIAL_SUPPLY(), allowance, approve, balanceOf, createTokens, decimals, endTime, name, unknown, owner, price, symbol, totalSupply... or not constant.

`now` will return the timestamp of the block ( actually `now` is an alias for `block.timestamp`) . So it's not real time. (And can be manipulated by miners in a certain extent).

The `fallback` function is kinda special, it has access to only `2300 gas`, no more .
``````function () public payable during_offering_time {