Use of an Anti-Pattern in CS2: Sequential if Statements with Exclusive Conditions

How can we teach students to use more readable code structures? How common is it for students to choose less readable (but still functional) alternatives? We explore these questions for a specific anti-pattern: using sequential if statements when conditions are exclusive (rather than using else-if or else). We created and validated an automated detector to identify this anti-pattern in student's code. Running the detector on 1,764 homework submissions (from 270 students in a CS2 class on data structures and algorithms) showed that this anti-pattern was common and varied by assignment: across 12 assignments, 3% to 50% of submissions used sequential ifs for exclusive cases. However, using this anti-pattern did not preclude using else-ifs: across assignments, up to 34% of the submissions used both forms. Further, students used sequential if statements in surprising ways, such as checking a condition and then the negation of that condition, indicating a more novice level of understanding than expected for an intermediate course. Hand-inspection of the detector-flagged cases suggests that sequential ifs for exclusive cases may be a code smell that can indicate larger problems with logic and abstraction.