Const in Class Method Definition

Can someone please explain to me why I'm getting the following compiler errors when I compile this code. I've been reading a C++ book, and it tells me that I should always use const at the end of the definition (int function() const;) which apparently says that the function I'm using it with won't be changing the values of variables, and that using const is a good way to help ensure bug-free programs.

These are the errors:

Code:

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Error: int Employee::getAge(void)' : overloaded member function not found in 'Employee'       
Error: int Employee::getYearOfService(void)' : overloaded member function not found in 'Employee'
Error: int Employee::Salary(void)' : overloaded member function not found in 'Employee'

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And the code here:

Code:

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#include <iostream>
 
using namespace std;
 
class Employee {
public:
        Employee();
        ~Employee();
        int getAge() const;
        void setAge(int Age);
        int getYearOfService() const;
        void setYearOfService(int YearOfService);
        int getSalary() const;
        void setSalary(int Salary);
private:
        int itsAge;
        int itsYearOfService;
        int itsSalary;
};
 
Employee::Employee(){
        itsAge = 0;
        itsYearOfService = 0;
        itsSalary = 0;
}
 
Employee::~Employee(){
 
}
 
 
int Employee::getAge(){
        return this->itsAge;
}
 
void Employee::setAge(int Age){
        this->itsAge = Age;
}
 
int Employee::getYearOfService(){
        return this->itsYearOfService;
}
 
void Employee::setYearOfService(int YearOfService){
        this->itsYearOfService = YearOfService;
}
 
int Employee::getSalary(){
        return this->itsSalary;
}
 
void Employee::setSalary(int Salary){
        this->itsSalary = Salary;
}
 
int main(){
        Employee Employee1;
        Employee Employee2;
        Employee1.setAge(21);
        Employee1.setSalary(26000);
        Employee1.setYearOfService(6);
        Employee2.setAge(33);
        Employee2.setSalary(39000);
        Employee2.setYearOfService(13);
        cout << "Employee 1 - Age: " << Employee1.getAge() << endl;
        cout << "Employee 1 - Salary: " << Employee1.getSalary() << endl;
        cout << "Employee 1 - Years Served: " << Employee1.getYearOfService() << endl << endl;
        cout << "Employee 2 - Age: " << Employee2.getAge() << endl;
        cout << "Employee 2 - Salary: " << Employee2.getSalary() << endl;
        cout << "Employee 2 - Years Served: " << Employee2.getYearOfService() << endl;
        cin.get();
}

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Thanks a lot! :D

You inadvertently put the solution in the thread title.

Code:

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class Employee {
public:
        int getYearOfService() const;

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Note that that's a class method (or member function in typical C++ terminology) declaration, not a definition. The definition is here:

Code:

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int Employee::getYearOfService(){
        return this->itsYearOfService;
}

---

and the problem is that there is no const there. It should be

Code:

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int Employee::getYearOfService() const {
        return this->itsYearOfService;
}

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You can have two functions with the same name and parameters, but different constness.

Ah I see now! Thanks a lot for clearing that up for me! :D