# ConstantsInProblems

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## Named Numerical Constants (Parameters) in Problems: PG Code Snippet

This code snippet shows the essential PG code to include named constants in a WeBWorK problem. Note that these are insertions, not a complete PG file. This code will have to be incorporated into the problem file on which you are working.

PG problem file Explanation
```Context("Numeric");
Context()->constants->add(k=>0.01);

# this means that student answers are
#    not reduced to the numerical value
#    specified in the Context
Context()->flags->set(
formatStudentAnswer=>'parsed'
);
```

No changes are needed in the tagging and description or initialization sections of the problem file. In the problem set-up section, we add to the Context the constants we're going to use. Here we define a constant k, and assign it a value that will be used when expressions involving k are evaluated. Do not set k=1, because if you do, then kx and x/k are equivalent, for example. Obviously, do not set k=0.

In this case we specified `constants->add()`, so that the constant k is added to existing constants in the problem. If we had used `constants->are()`, we would also remove all predefined constants from the Context (in a manner similar to the use of `variables->add()` and `variables->are()` when defining variables in a problem.

One other tweak that we might want to put in here is to reset a Context flag so that students' answers are not reduced to numerical values when they are previewed or submitted. This is done by setting the `formatStudentAnswer` flag, as shown.

```BEGIN_TEXT
\(f(x) = x-k\) (where \(k>0\) is constant)
is zero when \$BR
\(x = \)\{ ans_rule(15) \}
END_TEXT
```

In the text section of the problem we then ask a question involving the constant.

```ANS( Compute("k")->cmp() );
```

And in the answer and solution section of the file we can refer to the constant in the solution to the problem.