Advanced Placement (AP) Computer Science

What reflects a semantic error in a program?

1. The program's syntax is correct but doesn't work as intended.

2. The code does not compile.

3. There are no errors present.

4. The output does not match input exactly.

The correct answer is: The program's syntax is correct but doesn't work as intended.

A semantic error occurs when a program is syntactically correct—meaning it follows the rules of the programming language and successfully compiles—but produces incorrect results or behaves in an unintended manner. This type of error reflects a flaw in the logic of the program or the way the code is intended to function with its inputs and outputs. For instance, if a program is supposed to calculate the average of a set of numbers but mistakenly adds them instead, the syntax might be flawless, and the program would run without throwing errors, yet the results would not meet the expectations of the problem being solved. Thus, the program would not "work as intended," which is the defining feature of a semantic error. The other choices indicate different scenarios: a program that does not compile points to syntax errors, having no errors methodologically means the program is functioning properly, and output that does not match input can be a result of various issues but may not directly indicate a semantic error on its own without further context on expected behavior.