Robust and secure programming: syntax error

The idea

A syntax error is a breach of the grammar of the programming language, so the code cannot be translated into a runnable program. The translator checks the source against the language rules and reports the fault, often with a line number. Typical causes include a missing or mismatched bracket, a missing colon or quote mark, a misspelled keyword or variable name used before it is declared, and an operator used with the wrong number of operands. Because translation stops or fails, the program never executes, so a syntax error is detected before any output is produced. When you meet a scenario, check whether the code could ever be translated: if not, the fault is syntactic. Fixing it means correcting the grammar, not changing the algorithm's logic.

What earns the marks

• Defines a syntax error as code that breaks the grammar rules of the programming language.
• States that a syntax error prevents the program from being translated, so it cannot run.
• Gives a valid example such as a missing bracket, missing quote mark or misspelled keyword.
• Explains that the translator reports syntax errors, often identifying the line where the fault occurs.
• Distinguishes a syntax error from a logic error, which allows translation and execution but gives wrong output.

Common mistakes and how to put them right

• Confusing a syntax error with a logic error.

  Put it right: Is that a syntax error stops translation, whereas a logic error lets the program run but produce wrong results.

• Thinking a syntax error only appears when the program runs.

  Put it right: Is that it is detected during translation, before execution.

• Assuming any wrong output is a syntax error.

  Put it right: Is that wrong output from a running program points to a logic error.

Exam tips

• Check whether the described code could be translated at all; if not, it is a syntax error.
• Learn three concrete examples (missing bracket, missing quote, misspelled keyword) to recognise the category quickly.
• Remember the translator reports the fault, so link syntax errors to the translation stage rather than to runtime testing.