Types of Errors (Edexcel GCSE Computer Science)
Revision Note
Author
James WoodhouseExpertise
Computer Science
Syntax, Logic & Runtime Errors
Designing algorithms is a skill that must be developed and when designing algorithms, mistakes and issues will occur
There are three main categories of errors that when designing algorithms a programmer must be able to identify & fix, they are:
Syntax errors
Logic errors
Runtime errors
What is a syntax error?
A syntax error is an error that breaks the grammatical rules of a programming language and stops it from running
Examples of syntax errors are:
Typos and spelling errorsĀ
Missing or extra brackets or quotes
Misplaced or missing semicolons
Invalid variable or function names
Incorrect use of operators
Incorrectly nested loops & blocks of code
What is a logic error?
A logic error is where incorrect code is used that causes the program to run, but produces an incorrect output or result
Logic errors can be difficult to identify by the person who wrote the program, so one method of finding them is to use 'Trace Tables'
Examples of logic errors are:
Incorrect use of operatorsĀ (< and >)
Logical operator confusion (AND for OR)
Looping one extra time
Indexing arrays incorrectly (arrays indexing starts from 0)
Using variables before they are assigned
Infinite loops
What is a runtime error?
A runtime error is where an error causes a program to crash
Examples of runtime errors are:
Dividing a number by 0
Index out of the range of an array
Unable to read or write a drive
Identifying Logic Errors
Logic errors can be slightly challenging to locate compared to syntax errors
This is because the program will still run but will not produce the expected output that the programmer intended
The most obvious areas to check for logic errors are:
Logical operators (<, >, ==, !=)
Boolean operators (AND, OR, NOT)
To help demonstrate this skill, a snippet of program code is used
In this example, the incorrect logical operator has been used, OR instead of AND
The result means the else clause in the if statement would never be caught
At first glance, entering normal test data such as 14, the program works as intended
Entering erroneous data or boundary test data which is outside of the range would result in the error
When entering the age of 21, it still outputs that the user is in secondary school
Changing the OR to AND corrects the logic error
Worked Example
Dan is writing a program for maths students. To make sure that there are no logic errors in the program, Dan uses a test plan.
Describe what is meant by a logic error. [2]
Answer
The error does not prevent the program from running
But it does not produce the expected output / it does not do what the programmer intended
A reasonable example
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