How do I fix Error Code 1241: Operand should contain 1 column(s) in mysql query?

select firstName, lastName from students, courses, registration
where students.studentID = registration.studentID 
and courses.courseCode = registration.courseCode 
and gender = 'M' and courseName = 'Database Systems' 
in(select firstName, lastName 
from students, courses, registration
where students.studentID = registration.studentID 
and courses.courseCode = registration.courseCode 
and gender = 'M' and courseName = 'C++');``

I need to find the male students who have taken both Database Systems and C++, to do this I need to left join the tables students, registration, and courses,

Your in clause is missing some column try

select 
   firstName, lastName 
from students, courses, registration
where students.studentID = registration.studentID 
and courses.courseCode = registration.courseCode 
and gender = 'M' and courseName = 'Database Systems' 
and students.studentID
in (select studentID 
from students, courses, registration
where students.studentID = registration.studentID 
and courses.courseCode = registration.courseCode 
and gender = 'M' and courseName = 'C++');