The complete magic squares program follows. You can also view it online in the file YourSolverHome/examples/src/magicsq.cpp.

#include <ilsolver/ilosolverint.h>
ILOSTLBEGIN
 
int main(int argc, char* argv[]){
  IloEnv env;
  try {
    IloModel model(env);
    IloInt n = (argc > 1) ? atoi(argv[1]) : 5;
    IloInt sum = n*(n*n+1)/2;
    IloInt i, j;
    IloIntVarArray square(env, n*n, 1, n*n);
    model.add(IloAllDiff(env, square));
    // Constraints on rows
    for (i = 0; i < n; i++){
      IloExpr exp(env);
      for(j = 0; j < n; j++)
        exp += square[n*i+j];
      model.add(exp == sum);
      exp.end();
    }
    // Constraints on columns
    for (i = 0; i < n; i++){
      IloExpr exp(env);
      for(j = 0; j < n; j++)
        exp += square[n*j+i];
      model.add(exp == sum);
      exp.end();
    }
    // Constraint on 1st diagonal
    IloExpr exp1(env);
    for (i = 0; i < n; i++)
      exp1 += square[n*i+i];
    model.add(exp1 == sum);
    exp1.end();
    // Constraint on 2nd diagonal
    IloExpr exp2(env);
    for (i = 0; i < n; i++)
      exp2 += square[n*i+n-i-1];
    model.add(exp2 == sum);
    exp2.end();
    IloSolver solver(model);
    IloGoal goal = IloGenerate(env, square, IloChooseMinSizeInt);
    if (solver.solve(goal))
      {
      for (i = 0; i < n; i++){
        for (j = 0; j < n; j++)
          solver.out() << " " << solver.getValue(square[n*i+j]);
        solver.out() << endl;
      }
      solver.out() << endl;
    }
    else
      solver.out() << "No solution " << endl;
      solver.printInformation();
  }
  catch (IloException& ex) {
    cout << "Error: " << ex << endl;
  }
  env.end();
  return 0;
}
 

Results

You should get the following results, though the information displayed by IloSolver::printInformation will vary depending on platform, machine, configuration, and so on.

 1 2 13 24 25
 3 23 17 6 16
 20 21 11 8 5
 22 4 14 18 7
 19 15 10 9 12
 
Number of fails               : 791
Number of choice points       : 799
Number of variables           : 25
Number of constraints         : 13
Reversible stack (bytes)      : 8064
Solver heap (bytes)           : 20124
Solver global heap (bytes)    : 4044
And stack (bytes)             : 4044
Or stack (bytes)              : 4044
Search Stack (bytes)          : 4044
Constraint queue (bytes)      : 11152
Total memory used (bytes)     : 55516
Elapsed time since creation   : 0.11