Question

I’m working on a ASP.NET MVC (an older version) application and I have a form where students are assigned an adviser based on a major code AND by alpha of a student’s last name.

I am trying to implement the below code but it is showing red scribbles to & operator:

Error: operator ‘&’ cannot be applied to operands of type ‘System.Linq.IQueryable<Appointments.Models.MajorAdviserStudentAssignmentByAlpha>‘ and ‘lambda expression’ and ‘lambda expression’

var majorAssignmentByAlpha = FindAllMajorAdviserStudentAssignmentByAlphas()
    .Where(
           a => a.MajorString == student.StudentMajor) &
           (a => ((String.Compare(student.StudentLastName, a.AlphaStart) >= 0) &
                 (String.Compare(student.StudentLastName, a.AlphaEnd) <= 0))
    .FirstOrDefault());

if (majorAssignmentByAlpha != null)
    return majorAssignmentByAlpha.Adviser;

I would appreciate any help to understand what’s wrong here.
Thanks in advance!

Answer 1

I would like to add a correction here: actually both && and & are boolean AND operators in C# (when used with bool). However the former will do a short-circuit evaluation:

Consider A && B, if A is false then B will not be evaluated since the result will be false no matter what is the truthness of B.

And for the error you are getting, probably that’s because your & operator is comparing a boolean expression and a lambda expression (function). Try this

MajorAdviserStudentAssignmentByAlpha majorAssignmentByAlpha = FindAllMajorAdviserStudentAssignmentByAlphas().FirstOrDefault(
        a => a.MajorString == student.StudentMajor & String.Compare(student.StudentLastName, a.AlphaStart) >= 0 &
             String.Compare(student.StudentLastName, a.AlphaEnd) <= 0);

    if (majorAssignmentByAlpha != null)
        return majorAssignmentByAlpha.Adviser;