Undeclared identifier

[Jdmccull365]

are there modifications to this code because it is not compiling with multiple error codes of an undeclared identifier :

allowance[msg.sender][_spender] = _value;
emit Approval(msg.sender, _spender, _value);

require(_value <= allowance[_from][msg.sender]);
allowance[_from][msg.sender] = allowance[_from][msg.sender] - (_value);

all of these give error codes. How do you correct these ?