collection of variables in Z3 using C++ API - z3

Question

I want to define a collection of variables like "x_1" ... "X_1000", using Z3 C++ API. Can this be done using a for loop? I mean something of the form :
expr x[100] ;
for( i = 0; i < 1000 ; i++)
{ sprintf(str, "x_%d", i);
x[i] = c.bool_const(str);
}
solver s(c);
for( i = 0; i < 1000 ; i++)
s.add(x[i] >= 1)
If not, what should be the most elegant way to achieve this?

Answer 1

We can't write expr x[100] because the expr class does not have a constructor of the form expr::expr(). We should use the expr_vector instead. Here is an example (I also added it to the official C++ example in the Z3 distribution).
void expr_vector_example() {
context c;
const unsigned N = 10;
expr_vector x(c);
for (unsigned i = 0; i < N; i++) {
std::stringstream x_name;
x_name << "x_" << i;
x.push_back(c.int_const(x_name.str().c_str()));
}
solver s(c);
for (unsigned i = 0; i < N; i++) {
s.add(x[i] >= 1);
}
std::cout << s << "\n" << "solving...\n" << s.check() << "\n";
model m = s.get_model();
std::cout << "solution\n" << m;
}
UPDATE
I added new C++ APIs for creating universal and existential quantifiers using expr_vector.
The new APIs are already available in the unstable branch.
Here is an example:
void exists_expr_vector_example() {
std::cout << "exists expr_vector example\n";
context c;
const unsigned N = 10;
expr_vector xs(c);
expr x(c);
expr b(c);
b = c.bool_val(true);
for (unsigned i = 0; i < N; i++) {
std::stringstream x_name;
x_name << "x_" << i;
x = c.int_const(x_name.str().c_str());
xs.push_back(x);
b = b && x >= 0;
}
expr ex(c);
ex = exists(xs, b);
std::cout << ex << std::endl;
}