Types of Errors

Python reports SyntaxError and points near the problem. Other common syntax errors: missing colon after if, while, for or def; wrong indentation; mismatched quotes; using a keyword as a variable name.

An identifier is a name you give to a variable or function. Using a name that was never created — often a typing mistake like totl instead of total — is called an undeclared or undefined identifier.

• In compiled languages such as C, C++ and Java, variables must be declared before use. The compiler reports "undeclared identifier" before the program runs — it is treated as a compile-time (syntax) error.
• In Python, variables are created when first assigned, so the same mistake is only discovered when that line runs: a NameError — a runtime error.

The average of 60 and 80 should be 70, but the program prints 100.0. Division happens before addition, so it calculated 60 + 40. The fix is brackets: (mark1 + mark2) / 2. Logic errors are the hardest to find — only testing with known answers reveals them.