  One of the important scaffolding tasks in programming learning is writing a
line of code performing the necessary action. This allows students to practice
skills in a playground with instant feedback before writing more complex
programs and increases their proficiency when solving programming problems.
However, answers in the form of program code have high variability. Among the
possible approaches to grading and providing feedback, we chose template
matching. This paper reports the results of using regular-expression-based
questions with string completion hints in a CS1 course for 4 years with 497
students. The evaluation results show that Perl-compatible regular expressions
provide good precision and recall (more than 99\%) when used for questions
requiring writing a single line of code while being able to provide
string-completion feedback regardless of how wrong the initial student's answer
is. After introducing formative quizzes with string-completion hints to the
course, the number of questions that teachers and teaching assistants received
about questions in the formative quizzes dropped considerably: most of the
training question attempts resulted in finding the correct answer without help
from the teaching staff. However, some of the students use formative quizzes
just to learn correct answers without actually trying to answer the questions.
