J277 (9-1) Paper 2 Revision

High-Level vs. Low-Level

• High-Level Languages: Use English-like words (e.g., Python, C#). They can be used on different computer hardware. They *must* be translated (compiled or interpreted).
• Low-Level Languages: (e.g., Assembly Language). They are specific to hardware and allow direct memory manipulation.

Errors & Algorithms

• Syntax Error: The grammar of the program is wrong (e.g., `prnit("Hello")`). The translator will find this.
• Logic Error: The program runs, but does something unexpected (e.g., `total = num1 - num2` instead of adding).
• Arithmetic Operators: Know the pseudocode operators: `^` (power), `MOD` (modulus, finds remainder), `+`, `-`, `*`, `/`.

Sorting Algorithms

• Bubble Sort: Compares adjacent pairs of items (e.g., index 0 & 1, then 1 & 2) and swaps them if they are in the wrong order. It makes multiple passes through the list.
• Insertion Sort: Builds a sorted list at the start of the array. It takes one item at a time from the unsorted list and inserts it into the correct position in the sorted list.
• Similarities: Both can sort in ascending/descending order, and both are used to sort data in an array.
• `temp` variable: In both sorts, a `temp` variable is essential for swapping two values. It holds one value temporarily while the swap occurs.

Logic Gates

• AND gate: Output is 1 only if Input A AND Input B are both 1.
• OR gate: Output is 1 if Input A OR Input B (or both) are 1.
• NOT gate: Inverts the input. 1 becomes 0, 0 becomes 1.

Testing

• Why Test? To find and remove errors (bugs) and ensure the software meets the user's requirements.
• Test Data:
  • Normal Data: Sensible data that should be accepted (e.g., `5` in a 1-10 range).
  • Erroneous Data: Data that should be rejected (e.g., `hello` or `11` in a 1-10 range).
  • Boundary Data: Data at the limits of what is acceptable (e.g., `1` and `10` in a 1-10 range).

IDE Features & Validation

• IDE (Integrated Development Environment): Software to help programmers.
• Breakpoints: A tool that stops the program at a specific line so the programmer can check variable values.
• Stepping: A tool that lets the programmer run the code one line at a time.
• Validation: Checks to ensure data entered by a user is sensible and allowed (e.g., range check for a number, presence check to ensure it's not empty).

Data Types

• Integer: Stores whole numbers (e.g., `100`).
• Real: Stores numbers with decimal points (e.g., `10.5`).
• Boolean: Stores only `True` or `False`.
• String: Stores text, numbers, and symbols (e.g., `"Admin123"` or `"+44999"`).
• Char: Stores a single character (e.g., `'A'`).

Programming Constructs

• Sequence: Code running in order, one line after another.
• Selection: Using `IF...THEN...ELSE` to make a decision.
• Iteration: Using a loop (`FOR` or `WHILE`) to repeat code.
• Concatenation: Joining two strings together, often with `+`. (e.g., `sensorType + sensorNumber`).
• Casting: Converting a variable from one data type to another (e.g., `str(myInteger)` converts an integer to a string).

SQL (Structured Query Language)

SQL is used to manage and query data in a database.

• SELECT: Chooses which fields (columns) to display (e.g., `SELECT SensorID`).
• FROM: Chooses which table to get the data from (e.g., `FROM events`).
• WHERE: Filters the records (rows) based on a condition (e.g., `WHERE SensorType = "Door"`).
• AND: Used in a `WHERE` clause to add a second condition (e.g., `WHERE SensorType = "Door" AND Length > 20`).

2D Arrays & File Handling

• 2D Array: An array of arrays, like a table (e.g., `arrayEvents[1, 3]`). The first number is the row, the second is the column.
• File Handling: To save data, you must `open` a file, `write` to it, and then `close` it.
• Casting: When saving data to an array or file, you often need to convert data types. Converting an integer to a string (e.g., `str(Length)`) is called casting.