Override .ToString method c#

You are returning a string that just says the phrase _name + _number + _date + _salary.

What you likely wanted to do is build a string using those fields. If you wanted them all mushed together Concat would work, but it would be highly un-readable

public override string ToString()
{
    return String.Concat(_name, _number, _date, _salary);
}

However what would be better is to use Format and include labels with the values

public override string ToString()
{
    return String.Format("Name:{0}, Number:{1}, Date:{2}, Salary:{3}",_name, _number, _date, _salary);
}

---

If you are using C# 6 or newer you can use the following cleaner format

public override string ToString()
{
    return $"Name:{_name}, Number:{_number}, Date:{_date}, Salary:{_salary}";
}

Which is the exact same logic as the previous String.Format version.

The reason people override the ToString() method is to have a default string representation of your object, usually for display to the user or in a log or console, like this:

Console.WriteLine(yourClassObject);

If you do not override the ToString(), then its default implementation is to return the fully qualified name of your object, like this:

YourNamespace.YourClassName

By changing the inherited implementation (from System.Object), then you can make a nicer (read: prettier) representation, like this:

public override string ToString()
{
    return String.Format("This instance of my object has the following: Name = {0}, Number = {1}, Date = {2}, Salary = ${3}", _name, _number, _date, _salary);
}

Rather try something like

public override string ToString()
{
    return String.Format("Name : {0}, number {1}, date {2}, salary {3}",_name,_number,_date,_salary);
}

But it neads to be part of the class

so

class Employee
{
    private string _name;
    private string _number;
    private int _date;
    private int _salary;

    .....

    public override string ToString()
    {
        return String.Format("Name : {0}, number {1}, date {2}, salary {3}",_name,_number,_date,_salary);
    }
}

Have a look at String.Format Method

Replaces each format item in a specified string with the text equivalent of a corresponding object's value.