1. Component 1.6

2. Starter: Entry Ticket
Complete the Entry Ticket on Program Construction.
Extension:
Research the 5 stages of the compilation process and explain what they do (Lexical Analysis, Syntax Analysis, Semantic Analysis, Code Generation, and Optimisation).

3. Learning Intentions and Outcomes
To develop an understanding of how computer programs are constructed including the errors that may occur during construction.
Grade 4
Explain the purpose and use of Compilers, Interpreters, and Assemblers
Define the 5 compilation processes (Lexical Analysis, Syntax Analysis, Semantic Analysis, Code Generation, and Optimisation).
Describe different types of Program Construction Error
Grade 5-6
Describe different program errors and how they are caused
Explain the difference between Syntax and Logic Errors, providing examples for each
Grade 7
Explain what errors may occur at different stages of compilation
Explain the difference between translators and their benefits / drawbacks

4. Assessment Outcomes
Describe the purpose and give examples of the use of compilers, interpreters and assemblers
Explain the principal stages involved in the compilation process: lexical analysis, symbol table construction, syntax analysis, semantic analysis, code generation and optimisation
Describe and give examples of programing errors

5. Starter Discussion
The purpose of a translator is to translate Higher Levels of code into Lower Levels.

6. Starter Discussion
Assemblers Translate from Assembly Code to Machine Code Compilers Translate from High Level Code to Machine Code (the whole program at once). Interpreters Translate from High Level Code to Machine Code (one line at a time).

7. Translators
A translator changes (translates) a program written in one language into an equivalent program written in a different language. For example, a program written using the PASCAL programming language may be translated into a program written in one of the C programming languages using a translator

8. Assemblers
An assembler is a program which coverts the low level assembly programming language into machine code. The assembler does this by converting the one-word assembly instructions into an opcode, e.g. converting AND to It also allocates memory to variables, often resulting in an operand.

9. Translating High Level Code into Low Level
Compiler
Interpreter
Translates the whole program to produce the
Translates and executes one line at a time.
executable object code.
The object code is the version that the computer
The source code is the version that the computer
runs.
Faster run time because the program is translated
Slower run time because the program is translated
once, object code is run after that.
every time it is run.
Customers cannot see the actual code you wrote
If you distributed source code with an interpreter
when you distribute the program.
then customers would have your actual code.
Used for distributed software.
Used in development.
A compiler translates a high level programming language into machine code – it compiles every line of code at the same time.
An Interpreter translates a high level programming language into machine code – it translates each line of code separately. This helps programmers to debug their program and see which parts work and which do not!

10. Interpreters and compilers
Good for developing programs as you can execute parts of the program
Have to correct all the syntax errors before you can run the program
Slower execution as every line is translated before it is executed
Fast execution of object code
A user has to have the programming language and interpreter on their computer
Once the object code is produced, it can be installed and run on any computer
A user who has purchased your program can make changes and sell it on
A user who has purchased your program cannot see the source code

11. Compilation: There are 4 stages to Compiling a Program:
lexical analysis
syntax analysis
semantic analysis
code generation

12. Lexical Analysis Comments and unneeded spaces are removed.
Keywords, constants and identifiers are replaced by 'tokens'.
A symbol table is created which holds the addresses of variables, labels and subroutines

13. Syntax Analysis
Tokens are checked to see if they match the spelling and grammar expected, using standard language definitions. This is done by parsing each token to determine if it uses the correct syntax for the programming language.
If syntax errors are found, error messages are produced

14. Semantic Analysis
Variables are checked to ensure that they have been properly declared and used.
Variables are checked to ensure that they are of the correct data type, e.g. real values are not being assigned to integers.
Operations are checked to ensure that they are legal for the type of variable being used, e.g. you would not try to store the result of a division operation as an integer

15. Code Generation Machine code is generated.
Code optimisation may be employed to make it more efficient/faster/less resource intense

16. Grade 4 Exercises: Translating Code
Put the subheading “Translating Code into your book”
Explain what the following Translators do, provide pros and cons for each:
Compiler
Interpreter
Assembler
Define the following compilation processes:
Lexical Analysis
Syntax Analysis
Semantic Analysis
Code Generation
Optimisation

17. Program Errors
Error
Description
Example
Syntax
An error that occurs when a command does not follow the expected syntax of the language, e.g. when a keyword is incorrectly spelt
Incorrect: IF A ADN B Then
Correct: IF A AND B Then
Runtime/ executio n
An error that only occurs when the program is running and is difficult to foresee before a program is compiled and run
Program requests more memory when none is available, so the program crashes
Logical
An error that causes a program to output an incorrect answer (that does not necessarily crash the program)
An algorithm that calculates a person’s age from their date of birth, but ends up giving negative numbers
Error
Description
Example
Linking
An error that occurs when a programmer calls a function within a program and the correct library has not been linked to that program
When the square root function is used and the library that calculates the square root has not been linked to the program
Rounding
Rounding is when a number is approximated to nearest whole number/tenth/hundredth, etc.
34.5 rounded to nearest whole number is 35, an error of +0.5
Truncation
Truncating is when a number is approximated to a whole number/tenth/hundredth, etc. nearer zero
34.9 truncated to whole number is 34, an error of
-0.9

18. Grade 4 Exercises: Errors
Put the sub-heading “Errors” into your book
Define the following types of error:
Syntax
Logic
Run-Time
Linking
Rounding
Truncation
Explain the difference between a Syntax and a Logic Error
Extension
Move on to the exam questions – these need to be self assessed by the end of the lesson!

19. Grade 5-7 Exam Questions Complete them Self Assess them Stick them in
Bring them to me

20. Grade 8 Extension
Go into the A-Level Extension folder and have a go at the Grade D A Level Exercises!

21. Exit Ticket
Complete the Exit Ticket and Stick it in your books.

22. Homework Graded Exercises
Complete up to your year 11 target grade in the graded exercises
Pre-Reading
Make notes on Pages This is a lot so focus on these topics:
Flow Charts
Shapes
Decision
Loops
Pseudocode
Bubble Sort
Merge Sort
Searching