Error Types (SQA National 5 Computing Science): Revision Note

With syntax errors

RECEIVE name FROM (STRING) KEYBOARD
IF name = "Alice"        # missing THEN → prevents program from running
    SEND "Welcome Alice" TO DISPLAY
END IF

Corrected version

RECEIVE name FROM (STRING) KEYBOARD
IF name = "Alice" THEN
    SEND "Welcome Alice" TO DISPLAY
END IF

With syntax errors

# Syntax error: missing colon and wrong variable name
name = input("Enter your name")
if name == "Alice"
    print("Welcome Alis")

Corrected version

name = input("Enter your name: ")
if name == "Alice":
    print("Welcome Alice")

With logic error - If the pass mark is meant to include 50, this will give the wrong result

RECEIVE score FROM (INTEGER) KEYBOARD
IF score > 50 THEN
    SEND "You passed!" TO DISPLAY
ELSE
    SEND "You failed!" TO DISPLAY
END IF

Corrected version

IF score >= 50 THEN
    SEND "You passed!" TO DISPLAY
ELSE
    SEND "You failed!" TO DISPLAY
END IF

With logic error

score = int(input("Enter your score: "))

if score > 50:
    print("You passed!")
else:
    print("You failed!")

Corrected version

if score >= 50:
    print("You passed!")
else:
    print("You failed!")

With execution error - If the user enters 0 for num2, the program crashes.

RECEIVE num1 FROM (INTEGER) KEYBOARD
RECEIVE num2 FROM (INTEGER) KEYBOARD
SET answer ← num1 / num2
SEND "Answer: " & answer TO DISPLAY
# Program crashes if num2 = 0

Corrected version - with input validation

RECEIVE num1 FROM (INTEGER) KEYBOARD
RECEIVE num2 FROM (INTEGER) KEYBOARD

IF num2 = 0 THEN
    SEND "Error – cannot divide by zero" TO DISPLAY
ELSE
    SET answer ← num1 / num2
    SEND "Answer: " & answer TO DISPLAY
END IF

With execution error

# Runtime error: divide by zero
num1 = int(input("Enter a number: "))
num2 = int(input("Enter another number: "))

answer = num1 / num2
print("Answer:", answer)

Corrected version - with input validation

num1 = int(input("Enter a number: "))
num2 = int(input("Enter another number: "))

if num2 == 0:
    print("Error – cannot divide by zero")
else:
    answer = num1 / num2
    print("Answer:", answer)

Syntax

Breaks programming rules

Missing THEN or brackets

Program won’t run

Prevents the program from running

Logic

Incorrect algorithm

Wrong condition or operator

Wrong output

Produces an incorrect output

Execution (runtime)

Error during execution

Divide by zero, index error

Program crashes

Causes the program to crash