Sequence (Cambridge (CIE) O Level Computer Science)

Sequence

What is sequence?

• Sequence refers to lines of code which are run one line at a time

• The lines of code are run in the order that they written from the first line of code to the last line of code

• Sequence is crucial to the flow of a program, any instructions out of sequence can lead to unexpected behaviour or errors

Example 1

• A simple program to ask a user to input two numbers, number two is subtracted from number one and the result is outputted

• A simple swap of line 01 and line 02 would lead to an unexpected behaviour, the user would be prompted to input information without knowing what they should enter

Example 2

def calculate_area(length, width):
  return area
  area = length * width

# ------------------------------------------------------------------------
# Main program
# ------------------------------------------------------------------------

length = 5
width = 3
correct_area = calculate_area(length, width)
print(f"Correct area (length * width): {correct_area}")

• In the example, the sequence of instructions is wrong and would cause a runtime error

• In the calculate_area() function a value is returned before it is assigned

• The correct sequence is:

area = length * width
return area