I am building a CPLEX OPL model. I found error: Decision variable (or expression) "x" not allowed.

Here x is a decision variable and shown below:

dvar boolean x[N][CR];

and the Constraint is

forall(i in N, j in CR :x[i][j]==1) {

(j%2 == 0) => r[i] == 1;

(j%2 == 1) => r[i] == 0;

}

How I write this constraint correctly. Thanks in advance

Decision variables can't be used for slicing, as their values are unknown during model generation. The below is for illustration purpose (untested and probably not an efficient formulation):

forall(i in N, j in CR) {

(x[i][j]==1) => (r[i] == 1-j%2);

}