Sequence (Cambridge International IGCSE Computer Science)

Spec point — 8.1.4 · 4 (a) Understand and use the concept of sequence

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

• This function calculates the area of a rectangle

• Inputs:

  • length: The length of the rectangle
  • width: The width of the rectangle

• Returns:

  • The area of the rectangle

• 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

OR

area = length * width return area