почему появляются эти ошибки?

это весь код контракта

pragma solidity ^0.4.18;

interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) public; }

contract TokenERC20 {
    // Public variables of the token
    string public name;
    string public symbol;
    uint8 public decimals = 18;
    // 18 decimals is the strongly suggested default, avoid changing it
    uint256 public totalSupply;

    // This creates an array with all balances
    mapping (address => uint256) public balanceOf;
    mapping (address => mapping (address => uint256)) public allowance;

    // This generates a public event on the blockchain that will notify clients
    event Transfer(address indexed from, address indexed to, uint256 value);

    // This notifies clients about the amount burnt
    event Burn(address indexed from, uint256 value);

    /**
     * Constrctor function
     *
     * Initializes contract with initial supply tokens to the creator of the contract
     */
    function TokenERC20(uint256 initialSupply , string tokenName , string tokenSymbol) public {

        totalSupply assign = 250000000  ** uint256(18); // Update total supply with the decimal amount
        balanceOf[msg.sender] assign = totalSupply;                // Give the creator all initial tokens
        name assign = "PONTEM";                                   // Set the name for display purposes
        symbol assign = "PXM";                               // Set the symbol for display purposes
    }

    /**
     * Internal transfer, only can be called by this contract
     */
        /**
     * Internal transfer, only can be called by this contract
     */
    function _transfer(address _from, address _to, uint _value) internal {
        // Prevent transfer to 0x0 address. Use burn() instead
        require(_to != 0x0);
        // Check if the sender has enough
        require(balanceOf[_from] >= _value);
        // Check for overflows
        require(balanceOf[_to] + _value > balanceOf[_to]);
        // Save this for an assertion in the future
        uint previousBalances = balanceOf[_from] + balanceOf[_to];
        // Subtract from the sender
        require(!frozenAccount[_from]);                     // Check if sender is frozen
        require(!frozenAccount[_to]);                       // Check if recipient is frozen
        balanceOf[_from] -= _value;
        // Add the same to the recipient
        balanceOf[_to] += _value;
       emit Transfer(_from, _to, _value);
        // Asserts are used to use static analysis to find bugs in your code. They should never fail
        assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
    }

    /**
     * Transfer tokens
     *
     * Send `_value` tokens to `_to` from your account
     *
     * @param _to The address of the recipient
     * @param _value the amount to send
     */
    function transfer(address _to, uint256 _value) public {
        _transfer(msg.sender, _to, _value);
        require(!frozenAccount[msg.sender]);

    }    

    /**
     * Transfer tokens from other address
     *
     * Send `_value` tokens to `_to` in behalf of `_from`
     *
     * @param _from The address of the sender
     * @param _to The address of the recipient
     * @param _value the amount to send
     */
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        require(_value <= allowance[_from][msg.sender]);     // Check allowance
        allowance[_from][msg.sender] -= _value;
        _transfer(_from, _to, _value);
        return true;
    }

    /**
     * Set allowance for other address
     *
     * Allows `_spender` to spend no more than `_value` tokens in your behalf
     *
     * @param _spender The address authorized to spend
     * @param _value the max amount they can spend
     */
    function approve(address _spender, uint256 _value) public
        returns (bool success) {
        allowance[msg.sender][_spender] = _value;
        return true;
    }

    /**
     * Set allowance for other address and notify
     *
     * Allows `_spender` to spend no more than `_value` tokens in your behalf, and then ping the contract about it
     *
     * @param _spender The address authorized to spend
     * @param _value the max amount they can spend
     * @param _extraData some extra information to send to the approved contract
     */
    function approveAndCall(address _spender, uint256 _value, bytes _extraData)
        public
        returns (bool success) {
        tokenRecipient spender = tokenRecipient(_spender);
        if (approve(_spender, _value)) {
            spender.receiveApproval(msg.sender, _value, this, _extraData);
            return true;
        }
    }

    /**
     * Destroy tokens
     *
     * Remove `_value` tokens from the system irreversibly
     *
     * @param _value the amount of money to burn
     */
    function burn(uint256 _value) public returns (bool success) {
        require(balanceOf[msg.sender] >= _value);   // Check if the sender has enough
        balanceOf[msg.sender] -= _value;            // Subtract from the sender
        totalSupply -= _value;                      // Updates totalSupply
      emit  Burn(msg.sender, _value);
        return true;
    }

    /**
     * Destroy tokens from other account
     *
     * Remove `_value` tokens from the system irreversibly on behalf of `_from`.
     *
     * @param _from the address of the sender
     * @param _value the amount of money to burn
     */
    function burnFrom(address _from, uint256 _value) public returns (bool success) {
        require(balanceOf[_from] >= _value);                // Check if the targeted balance is enough
        require(_value <= allowance[_from][msg.sender]);    // Check allowance
        balanceOf[_from] -= _value;                         // Subtract from the targeted balance
        allowance[_from][msg.sender] -= _value;             // Subtract from the sender's allowance
        totalSupply -= _value;                              // Update totalSupply
       emit Burn(_from, _value);
        return true;

    } mapping (address => bool) public frozenAccount;
    event FrozenFunds(address target, bool frozen);

    function freezeAccount(address target, bool freeze) public {
        frozenAccount[target] = freeze;
      emit  FrozenFunds(target, freeze);

    }    uint256 public sellPrice;
    uint256 public buyPrice;

    function setPrices(uint256 newSellPrice, uint256 newBuyPrice)  public {
        sellPrice = newSellPrice;
        buyPrice = newBuyPrice;

    }/// @notice Buy tokens from contract by sending ether
    function buy() payable public returns(uint amount) {
        amount = msg.value / buyPrice;               // calculates the amount
        require(balanceOf[this] >= amount);               // checks if it has enough to sell
        require(balanceOf[msg.sender] >= amount * buyPrice); // checks if sender  has enough ether to buy
        balanceOf[msg.sender] += amount;                  // adds the amount to buyer's balance
        balanceOf[this] -= amount;                        // subtracts amount from seller's balance
        _transfer(this, msg.sender, amount);              // makes the transfers
        return amount;
    }

    /// @notice Sell `amount` tokens to contract
    /// @param amount amount of tokens to be sold
    function sell(uint256 amount) public returns(uint revenue) {
        require(this.balance >= amount * sellPrice);      // checks if the contract has enough ether to buy
        require(balanceOf[msg.sender] >= amount);         // checks if it has enough to sell
        balanceOf[this] += amount;                  // adds the amount to buyer's balance
        balanceOf[msg.sender] -= amount;                        // subtracts amount from seller's balance
        revenue = amount * sellPrice;
        _transfer(msg.sender, this, amount);              // makes the transfers
        require(msg.sender.send(revenue));                // sends ether to the seller: it's important to do this last to prevent recursion attacks
       return revenue;
    }


}

новые ошибки это

ошибка 1:

Предупреждение: определение конструкторов как функций с тем же именем, что и у контракта, устарело. Вместо этого используйте «конструктор (...) { ... }».

 function TokenERC20(uint256 initialSupply , string tokenName , string tokenSymbol) public {

ошибка2:

browser/ballot.sol:30:9: Предыдущее объявление находится здесь:

totalSupply assign = 250000000  ** uint256(18); // Update total supply with the decimal amount
^----------------^

browser/ballot.sol:31:9: TypeError: Имя должно относиться к структуре, перечислению или контракту.

balanceOf[msg.sender] assign = totalSupply;// Give the creator all initial tokens
^-------^

browser/ballot.sol:32:9: DeclarationError: Идентификатор уже объявлен.

  name assign = "PONTEM";     // Set the name for display purposes
  ^---------^

browser/ballot.sol:33:9: DeclarationError: Идентификатор уже объявлен.

 symbol assign = "PXM";// Set the symbol for display purposes
 ^-----------^