Warnings by deploying ERC20 token sol, - deployment

Question

I want to deploy my contract but I have so many warnings, I don't know every meaning.
Gas requirement of function SpastToken.increaseApproval(address,uint256) high. (11 times in other functions)
BasicToken.balanceOf(address) : Variables have very similar names balance and balances. Note: Modifiers are currently not considered by this static analysis.
Use assert(x) if you never ever want x to be false, not in any circumstance (apart from a bug in your code). Use require(x) if x can be false, due to e.g. invalid input or a failing external component.
contract Ownable {
address public owner;
event OwnershipTransferred(address indexed previousOwner, address indexed
newOwner);
constructor() public {
owner = msg.sender;
}
modifier onlyOwner() {
require(msg.sender == owner);
_;
}
function transferOwnership(address newOwner) public onlyOwner {
require(newOwner != address(0));
emit OwnershipTransferred(owner, newOwner);
owner = newOwner;
}
}
contract ERC20Basic {
function totalSupply() public view returns (uint256);
function balanceOf(address who) public view returns (uint256);
function transfer(address to, uint256 value) public returns (bool);
event Transfer(address indexed from, address indexed to, uint256 value);
}
/**
* #title ERC20 interface
*/
contract ERC20 is ERC20Basic {
function allowance(address owner, address spender) public view returns
(uint256);
function transferFrom(address from, address to, uint256 value) public
returns (bool);
function approve(address spender, uint256 value) public returns (bool);
event Approval(address indexed owner, address indexed spender, uint256
value);
}
/**
* #title Basic token
*/
contract BasicToken is ERC20Basic {
using SafeMath for uint256;
mapping(address => uint256) balances;
uint256 totalSupply_;
function totalSupply() public view returns (uint256) {
return totalSupply_;
}
function transfer(address _to, uint256 _value) public returns (bool) {
require(_to != address(0));
require(_value <= balances[msg.sender]);
balances[msg.sender] = balances[msg.sender].sub(_value);
balances[_to] = balances[_to].add(_value);
emit Transfer(msg.sender, _to, _value);
return true;
}
function balanceOf(address _owner) public view returns (uint256 balance) {
return balances[_owner];
}
}
/**
* #title Standard ERC20 token
*/
contract StandardToken is ERC20, BasicToken {
mapping (address => mapping (address => uint256)) internal allowed;
function transferFrom(address _from, address _to, uint256 _value) public
returns (bool) {
require(_to != address(0));
require(_value <= balances[_from]);
require(_value <= allowed[_from][msg.sender]);
balances[_from] = balances[_from].sub(_value);
balances[_to] = balances[_to].add(_value);
allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
emit Transfer(_from, _to, _value);
return true;
}
function approve(address _spender, uint256 _value) public returns (bool) {
allowed[msg.sender][_spender] = _value;
emit Approval(msg.sender, _spender, _value);
return true;
}
function allowance(address _owner, address _spender) public view returns
(uint256) {
return allowed[_owner][_spender];
}
function increaseApproval(address _spender, uint _addedValue) public returns
(bool) {
allowed[msg.sender][_spender] = allowed[msg.sender]
[_spender].add(_addedValue);
emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
return true;
}
function decreaseApproval(address _spender, uint _subtractedValue) public
returns (bool) {
uint oldValue = allowed[msg.sender][_spender];
if (_subtractedValue > oldValue) {
allowed[msg.sender][_spender] = 0;
} else {
allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
}
emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
return true;
}
}
contract SpastToken is StandardToken, Ownable {
string public name;
string public symbol;
uint8 public decimals;
uint256 public initialSupply;
constructor() public {
name = 'SPAST-Coin';
symbol = 'SPAS';
decimals = 18;
initialSupply = 100000000 * 10 ** uint256(decimals);
totalSupply_ = initialSupply;
balances[owner] = initialSupply;
emit Transfer(0x0, owner, initialSupply);
}
}

Answer 1

I think these warnings are pretty self explanatory. Except maybe the last one about the assertion. That one basically says that you should use assert() to check for logic errors in your code(that would be something you did wrong), whereas you should use require() to check if the inputs are legal or not(that would be the callers mistake). I don't think the rest of the warnings can be explained further, consider googling them. The one with the variable names however is just there to help you avoid typos from similar variable names and will not affect execution in any way. The modifiers warnings that do not appear here try to tell you that you could have stricter modifiers for your functions which again would make reading the code simpler.