1.9. Semantic Errors¶

The third type of error is the semantic error. If there is a semantic error in your program, it will run successfully in the sense that the computer will not generate any error messages. However, your program will not do the right thing. It will do something else. Specifically, it will do what you told it to do.

The problem is that the program you wrote is not the program you wanted to write. The meaning of the program (its semantics) is wrong. Identifying semantic errors can be tricky because it requires you to work backward by looking at the output of the program and trying to figure out what it is doing.

Check your understanding

intro-9-1: Which of the following is a semantic error?
• (A) Attempting to divide by 0.
• A semantic error is an error in logic. In this case the program does not produce the correct output because the problem is not solved correctly. This would be considered a run-time error.
• (B) Forgetting a semi-colon at the end of a statement where one is required.
• A semantic error is an error in logic. In this case the program does not produce the correct output because the code can not be processed by the compiler or interpreter. This would be considered a syntax error.
• (C) Forgetting to divide by 100 when printing a percentage amount.
• This will produce the wrong answer because the programmer implemented the solution incorrectly. This is a semantic error.