Faults & errors (Cambridge (CIE) AS Computer Science): Revision Note

FUNCTION GenerateUsername(FirstName STRING, LastName : STRING) RETURNS STRING
   DECLARE Username : STRING
   Username = LEFT(FirstName, 1) & LEFT(LastName, 3)
   RETURN Username
ENDFUNCTION

PROCEDURE Main()
   DECLARE FirstName : STRING
   DECLARE LastName : STRING
   DECLARE Username : STRING

   OUTPUT "Enter your first name: "
   INPUT FirstName
   OUTPUT "Enter your last name: "
   INPUT LastName
   Username ← GenerateUsername[FirstName, LastName]
   OUTPUT "Here is a suggested username: ", Username
ENDPROCEDURE

// Main program
CALL Main

FUNCTION GenerateUsername(FirstName : STRING, LastName : STRING) RETURNS STRING
   DECLARE Username : STRING
   Username ← LEFT(FirstName, 1) & LEFT(LastName, 3)
   RETURN Username
ENDFUNCTION

PROCEDURE Main()
   DECLARE FirstName : STRING
   DECLARE LastName : STRING
   DECLARE Username : STRING

   OUTPUT "Enter your first name: "
   INPUT FirstName
   OUTPUT "Enter your last name: "
   INPUT LastName
   Username ← GenerateUsername(FirstName, LastName)
   OUTPUT "Here is a suggested username: ", Username
ENDPROCEDURE

// Main program
CALL Main()

• FUNCTION GenerateUsername(FirstName STRING, ...)

  • Missing colon between the parameter name and its data type

  • Should be FirstName : STRING

• Username = LEFT(...)

  • Uses = instead of the assignment operator ←

  • Should be Username ← ...

• Username ← GenerateUsername[FirstName, LastName]

  • Square brackets [] used instead of parentheses () for a function call

  • Should be GenerateUsername(FirstName, LastName)

• CALL Main

  • Missing parentheses in the procedure call

  • Should be CALL Main()

FUNCTION CalculateArea(Length : REAL, Width : REAL) RETURNS REAL
   DECLARE Area : REAL
   // Checks for valid dimensions and calculates area
   IF Length > 0 OR Width > 0 THEN
      Area ← Width - Length
   ELSE
      OUTPUT "Length and width must be positive values."
      Area ← 0
   ENDIF
   RETURN Area
ENDFUNCTION

PROCEDURE Main()
   DECLARE Length : REAL
   DECLARE Width : REAL
   DECLARE Area : REAL

   OUTPUT "Enter the length of the rectangle: "
   INPUT Length
   OUTPUT "Enter the width of the rectangle: "
   INPUT Width
   Area ← CalculateArea(Length, Width)
   OUTPUT "The area of the rectangle is ", Area, " square units."
ENDPROCEDURE

// Main program
CALL Main()

IF Length > 0 OR Width > 0 THEN

The check allows one value to be negative or zero, which is not valid

Should be IF Length > 0 AND Width > 0 THEN

Area ← Width - Length

Incorrect calculation: subtracts instead of multiplying to find the area

Should be Area ← Length * Width

FUNCTION AverageMark(Total : INTEGER, NumberOfStudents : INTEGER) RETURNS REAL
   RETURN Total / NumberOfStudents
ENDFUNCTION

PROCEDURE Main()
   DECLARE Total : INTEGER
   DECLARE NumberOfStudents : INTEGER
   DECLARE Average : REAL

   OUTPUT "Enter the total of all the marks: "
   INPUT Total
   OUTPUT "Enter the number of students: "
   INPUT NumberOfStudents
   Average ← AverageMark(Total, NumberOfStudents)
   OUTPUT "The average mark is ", Average
ENDPROCEDURE

// Main program
CALL Main()

Replace the run-time error table row with:
<tr><td>`RETURN Total / NumberOfStudents`</td><td>If the user enters 0 for the number of students, the program tries to divide by zero and crashes while it is running</td><td>Check the value before dividing:<br>`IF NumberOfStudents > 0 THEN`<br>`   RETURN Total / NumberOfStudents`<br>`ELSE`<br>`   RETURN 0`<br>`ENDIF`</td></tr>

RETURN Total / NumberOfStudents

If the user enters 0 for the number of students, the program tries to divide by zero and crashes while it is running

Check the value before dividing:

IF NumberOfStudents > 0 THEN

RETURN Total / NumberOfStudents

ELSE

RETURN 0

ENDIF