GymInstructors/GymInstructors.sol

pragma solidity ^0.4.24;

contract GymInstructors{

  address owner;

  function GymInstructor() public{
    owner = msg.sender;
  }

  modifier onlyOwner{
    require(msg.sender == owner);
    _;
  }

  struct Instructor{
    string fName;
    string lName;
    uint age;
    string field;
  }

  mapping(address => Instructor) instructors;
  address[] public instructorAccounts;


  //sets the info for a new instructor
  function setInstructor(address _address, string _fName, string _lName, uint _age, string _field)onlyOwner public{
    var instructor = instructors[_address];

    instructor.fName = _fName;
    instructor.lName = _lName;
    instructor.age = _age;
    instructor.field = _field;

    instructorAccounts.push(_address) -1 ;
  }

  //returns all the instructor accounts
  function getInstructors() public returns(address[]){
    return instructorAccounts;
  }

  //returns the info of an instructor specified by address
  function getInstructor(address _address) view public returns(string fn, string ln, uint a, string fld){
    return(instructors[_address].fName, instructors[_address].lName, instructors[_address].age, instructors[_address].field);
  }

  //returns the total number of available instructors
  function countAllInstructors() public returns(uint){
    return instructorAccounts.length;
  }

  //returns true if a certain instructor is specialized in the given field, false otherwise
  function checkField(address _address, string _field) public returns(bool){
    require(keccak256(abi.encodePacked(instructors[_address].field)) == keccak256(abi.encodePacked(_field)));
    return true;
  }
}