Identifying Errors | Computer for GCSE/IGCSE - Year 11 PDF Download

Identifying Errors

Errors in algorithms can be pinpointed through the utilization of trace tables, along with manual scanning and debugging of code.
The two categories of errors are as follows:

Syntax error 

• Syntax pertains to the grammar of a language, ensuring correct word order and spelling.
• In contrast to computer programs, syntax errors in flowcharts and pseudocode don't lead to algorithm failure but can complicate readability and comprehension.
• Converting flowcharts and pseudocode into actual programming code may pose challenges if the original flowcharts and pseudocode are hard to interpret.

Logical Errors

• Logical errors occur when the program completes execution but produces incorrect output.
• Flowcharts and pseudocode, unlike actual programs, do not crash during dry runs. However, they can still lead to logic errors by generating inaccurate output.
• Fixing logical errors is challenging as developers need to reevaluate their logic and processes. Without a clear understanding of the problem, producing a correct solution becomes difficult.

Below is an algorithm that prompts the user to input their age to ascertain the movie rating they are eligible to watch at the cinema.
There are syntax and logical errors within this pseudocode.
OUTPUT Age
INPUT “Enter an age”
IF Age > 18
THEN
OUTPUT “You can watch an 18 movie”
ELSE
IF Age > 15
  THEN
OUTPUT “You can watch a 15 movie
ELSE
IF Age > 12
  THEN
OUTPUT “You can watch a 12 movie”
ELSE
IF Age < 9
THEN
OUTPUT “You can watch a PG movie”
ELSE
OUTPUT “You can watch a U movie”
END IF
ENDIF
ENDIF
ENDIF

• Syntax and logic: Both "OUTPUT Age" and "INPUT “Enter an age”" contain syntax and logical errors.
  • Syntax: "Age" lacks a value for display, making it incorrect for "OUTPUT" to display it. Additionally, "INPUT" lacks a variable to store the data since strings cannot store data.
  • Logical: Both commands are in the wrong order. "OUTPUT Age" should be "OUTPUT “Enter an age”", and "INPUT “Enter an age”" should be "INPUT Age".
• Syntax: The first IF statement lacks "THEN".
• Syntax: The output message "You can watch a 15 movie" lacks a closing quote.
• Logic: "Age < 9" should be "Age > 9" to align with the logic of the other IF statement.
• Syntax: The first IF statement lacks "ENDIF".