In many cases it is even unnecessary to allocate binary variables explicitly in order to gain the benefit of linear constraints within logical expressions. For example, optimizing how many items appear in a solution is often an issue in practical problems. Questions of counting (how many?) can be represented formally as cardinality constraints.

Suppose that your application includes three variables, each representing a quantity of one of three products, and assume further that a good solution to the problem means that the quantity of at least two of the three products must be greater than 20. Then you can represent that idea in your application, like this:

IloNumVarArray x(env, 3, 0, 1000);
model.add((x[0] >= 20) + (x[1] >= 20) + (x[2] >= 20) >= 2);