[Help-glpk] Strange Error with if/then/else

[Jonathan Klein]

Hi,

i havbe a very simple Problem like this:

set PEOPLE;
var x{i in PEOPLE} binary;
maximize Anzahl : sum{i in PEOPLE} (if x[i]==1 then 1 else 0);
data;
set LEUTE:=Hans Joachen Peter Klaus;
end;

And i get the Error: operator preceding == has invalid type

I know, that this problem doesn't make sense, but i have i somewhat more 
complex problem in wich i get the same error:




# Berufsinformationstag

set STUDENT;#i
set CHOICE;#j
set COURSE;#k
set GROUP;#l

param Student_Choice {i in STUDENT, j in CHOICE} symbolic in COURSE;# 
Welcher Schüler welche Wünsche hat
#param Course_Minimum {k in COURSE};#Wie viele Schüler eine 
Veranstaltung minimal braucht
#param Course_Maximum {k in COURSE};#Wie viele Schüler eine 
Veranstaltung haben darf
param Satisfaction {j in CHOICE};#für jeden wunsch die Menge, wie 
glücklich er ist


var TimeTable{k in COURSE, l in GROUP}, binary;
var StudentDistribution {i in STUDENT, k in COURSE, l in GROUP} binary ;

# wenn sich der schüler die aktuelle veranstaltung wünscht und in der 
veranstaltung in dieser gruppe ist
maximize z: sum{i in STUDENT, l in GROUP, k in COURSE, j in CHOICE}
                        (if 1==StudentDistribution[i,k,l]
                        and k==Student_Choice[i, j]
                        then Satisfaction[k] else 0);





So i have Students that are in different Courses, in 1 Course per Group. 
They coose 6 Courses and will be in 4 (1 in each group). If they are in 
a grout that the have choosen, they are happy.
So i have to check for every Choice of every Student in every Course in 
every Group if the student is in this course in this group and if he had 
choosen it. If so, he gets as much happiness as his choice had importance.

At the end i need to know form every Student in which courses he ist an 
which courses in which group have to take place, so i have choosen the 
binary variables.

I dont konw why the types should not match, because StudentDistribution 
ist binary, so i can only be 0 or 1 an Student_Choice has to be a COURSE.

I studiet the language reference manual for a long time and looked at 
many examples with if/then/else but i still have no idea what i'm doing 
wrong.

PS: I use C++ for 5 years now, but im relativly new to GNU MathProg :(

I would be very gald for every help.

Jonathan