Identifying Errors (Cambridge International IGCSE Computer Science): Exam Questions

An algorithm allows a user to input their password and checks that there are at least eight characters in the password. Then, the user is asked to re-input the password to check that both inputs are the same. The user is allowed three attempts at inputting a password of the correct length and a matching pair of passwords.

The pre-defined function LEN(X) returns the number of characters in the string, X

Identify the three errors in the pseudocode and suggest a correction to remove each error.

An algorithm has been written in pseudocode to allow some numbers to be input. All the positive numbers that are input are totalled and this total is output at the end. An input of 0 stops the algorithm.

Identify the four errors in the pseudocode and suggest a correction for each error.

An algorithm has been written in pseudocode to calculate a check digit for a four-digit number. The algorithm then outputs the five-digit number including the check digit. The algorithm stops when –1 is input as the fourth digit.

Identify the three errors in the pseudocode and suggest a correction for each error.

An algorithm has been written in pseudocode to input some numbers. It only outputs any numbers that are greater than or equal to 100. The number 999 is not output and stops the algorithm.

INPUT Number WHILE Numbers <> 999 DO IF Number > 100 THEN OUTPUT Number ENDIF ENDWHILE OUTPUT Number

Identify the four errors in the pseudocode and suggest corrections.

Extract:

An algorithm has been written in pseudocode to input some numbers. It only outputs any numbers that are greater than or equal to 100. The number 999 is not output and stops the algorithm.

INPUT Number

WHILE Numbers <> 999 DO

IF Number > 100

  THEN

     OUTPUT Number

ENDIF

ENDWHILE

OUTPUT Number

The four errors in the pseudocode are:

Numbers

• … should be Number

IF Number > 100

• … should be IF Number >= 100

INPUT Number missing from inside the loop

• … insert INPUT Number after the ENDIF statement

The final OUTPUT Number is not needed

• … remove it

Write a pseudocode statement to change the corrected algorithm to output all numbers between 100 and 200 inclusive.

You do not need to rewrite the whole algorithm

This section of program code asks for 80 numbers between 100 and 1000 inclusive to be entered. The pseudocode checks that the numbers are in the correct range and then stores the valid numbers in an array. It counts how many of the numbers are larger than 500 and then outputs the result when finished.

There are four lines of code that contain errors.

State the line number for each error and write the correct code for that line.