Programming Errors

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

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

  
  

  • 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.
• 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.