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When developing programs there are two types of error (bug) that often occur:

• syntax errors
• logic errors

Syntax errors

A syntax error occurs when code written does not follow the rules of the programming language. Examples include:

• misspelling a statement, eg writing pint instead of print
• using a variable before it has been declared
• missing brackets, eg opening a bracket but not closing it

A program will not run if it has syntax errors. Any such errors must be fixed first. A good integrated development environment (IDE) will usually point out any syntax errors to the programmer.

Logic errors

A logic error is an error in the way a program works. The program simply does not do what it is expected to do.

Logic errors can have many causes, such as:

• incorrectly using logical operators, eg expecting a program to stop when the value of a variable reaches 5, but using <5 instead of <=5
• incorrectly using Boolean operators
• unintentionally creating a situation where an infinite loop may occur
• incorrectly using brackets in calculations
• unintentionally using the same variable name at different points in the program for different purposes
• referring to an element in an array that falls outside of the scope of the array

Unlike a syntax error, a logic error will not usually stop a program from running. Instead the program will run but not function as expected.