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Identify Locate And Correct Program Errors Edexcel

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Exam code:1CP2

How do you identify, locate & correct program errors?

In the exam students are expected to be able to:
- Fix syntax errors in code
- Use test data to identify run-time and logic errors which undetected would prevent code from functioning correctly
A level-based mark scheme for functionality awards marks for error-free, robust solutions

Examiner Tips and Tricks

Before working through the examples below, it is important you fully understand the different types of errors in programming. To revise them click here

Syntax Errors

Task

Locate the syntax errors and correct them so that the program works

Python code – with syntax errors
`def generate_username(first_name, last_name)` “”” Generates a username based on the provided first and last name. Inputs: first_name (str): User’s first name. last_name (str): User’s last name. Returns: str: A username combining initials and the first 3 characters of the last name. “”” `username = f"{first_name[0]}{last_name[0]}{last_name[:3]}"` `return username` `def main():` # ———————————————————————– # Prompts the user for personal information and displays a suggested username # ———————————————————————– `first_name = imput("Enter your first name: ")` `last_name = input("Enter your last name: ")` `usdrname = generate_username(first_name, last_name)` `print(f"Here's a suggested username: {username}")` # ———————————————————————— # Main program # ———————————————————————— `main`
Python code – without syntax errors
`def generate_username(first_name, last_name):` “”” Generates a username based on the provided first and last name. Inputs: first_name (str): User’s first name. last_name (str): User’s last name. Returns: str: A username combining initials and the first 3 characters of the last name. “”” `username = f"{first_name[0]}{last_name[0]}{last_name[:3]}"` `return username` `def main():` # ———————————————————————– # Prompts the user for personal information and displays a suggested username # ———————————————————————– `first_name = input("Enter your first name: ")` `last_name = input("Enter your last name: ")` `username = generate_username(first_name, last_name)` `print(f"Here's a suggested username: {username}")` # ———————————————————————— # Main program # ———————————————————————— `main()`
Syntax errors
Missing semicolon `def generate_username(first_name, last_name)` Incorrectly spelt function name `first_name = imput("Enter your first name: ")` Typo in variable name `usdrname = generate_username(first_name, last_name)` Missing parenthesis `main`

Logic & Runtime Errors

Task

Use suitable test data to identify and locate logic & runtime errors in the following program

Python code
`def calculate_area(length, width):` “”” Calculates the area of a rectangle Inputs: length (float): The length of the rectangle (positive value) width (float): The width of the rectangle (positive value) Returns: float: The calculated area of the rectangle Raises: ValueError: If either length or width is non-positive “”” `if length < 0 or width < 0:` `raise ValueError("Length and width must be positive values.")` `area = length * width` `return area` `def main():` # ———————————————————————– Prompts the user for rectangle dimensions and prints the calculated area # ———————————————————————– `try:` `length = float(input("Enter the length of the rectangle: "))` `width = float(input("Enter the width of the rectangle: "))` # Call the area calculation function `area = calculate_area(length, width)` `print(f"The area of the rectangle is approximately {area:.2f} square units.")` `except ValueError as error:` `print(f"Error: {error}")` # ———————————————————————– # Main program # ———————————————————————– `main()`

Python code

def calculate_area(length, width):

“””

Calculates the area of a rectangle

Inputs:

length (float): The length of the rectangle (positive value)

width (float): The width of the rectangle (positive value)

Returns:

float: The calculated area of the rectangle

Raises:

ValueError: If either length or width is non-positive

“””

if length < 0 or width < 0:

raise ValueError("Length and width must be positive values.")

area = length * width

return area

def main():

# ———————————————————————–

Prompts the user for rectangle dimensions and prints the calculated area

# ———————————————————————–

try:

length = float(input("Enter the length of the rectangle: "))

width = float(input("Enter the width of the rectangle: "))

# Call the area calculation function

area = calculate_area(length, width)

print(f"The area of the rectangle is approximately {area:.2f} square units.")

except ValueError as error:

print(f"Error: {error}")

# ———————————————————————–

# Main program

# ———————————————————————–

main()

Logic errors

Test number	Test data	Expected outcome	Actual outcome	Changes needed? (Y/N)
1	Length = 5 Width = 5	“The area of the rectangle is approximately 25 square units.”	“The area of the rectangle is approximately 25.00 square units.”	N
2	Length = 10 Width = 0	“Length and width must be positive values.”	“The area of the rectangle is approximately 0.00 square units.”	Y should not accept 0 input as not positive

Test number

Test data

Expected outcome

Actual outcome

Changes needed? (Y/N)

Length = 5

Width = 5

“The area of the rectangle is approximately 25 square units.”

“The area of the rectangle is approximately 25.00 square units.”

Length = 10

Width = 0

“Length and width must be positive values.”

“The area of the rectangle is approximately 0.00 square units.”

Y
should not accept 0 input as not positive

Logic error located on line if length < 0 or width < 0:
Logic error identified in expression < 0, should be <= 0 so that 0 is not accepted as valid input for length or width

Runtime errors

Test number	Test data	Expected outcome	Actual outcome	Changes needed? (Y/N)
1	Length = 10 Width = 10	“The area of the rectangle is approximately 100 square units.”	“The area of the rectangle is approximately 100.00 square units.”	N
2	Length = “abc” Width = 0	“Program could not convert string to float, try again”	Program crashed	Y should give error message and ask user to enter again

Test number

Test data

Expected outcome

Actual outcome

Changes needed? (Y/N)

Length = 10

Width = 10

“The area of the rectangle is approximately 100 square units.”

“The area of the rectangle is approximately 100.00 square units.”

Length = “abc”

Width = 0

“Program could not convert string to float, try again”

Program crashed

Y
should give error message and ask user to enter again

Runtime error located in

try:

length = float(input("Enter the length of the rectangle: "))

width = float(input("Enter the width of the rectangle: "))

# Call the area calculation function

area = calculate_area(length, width)

print(f"The area of the rectangle is approximately {area:.2f} square units.")

except ValueError as error:

print(f"Error: {error}")

Runtime error identified as missing iteration (while loop) so program does not ask user to enter width and height again
Corrected code now includes a while loop

while True:

try:

length = float(input("Enter the length of the rectangle: "))

width = float(input("Enter the width of the rectangle: "))

# Call the area calculation function

area = calculate_area(length, width)

print(f"The area of the rectangle is approximately {area:.2f} square units.")

break # Exit the loop if successful

except ValueError as error:

print(f"Error: {error}")

print("Please enter positive values for length and width.")

Computer Science GCES EDEXCEL

Identify Locate And Correct Program Errors Edexcel

How do you identify, locate & correct program errors?

Examiner Tips and Tricks

Syntax Errors

Task

Logic & Runtime Errors

Task

Logic errors

Runtime errors

Responses