Topic 7.2 Programming

Topic 7.2 Programming

1. Why translators, compilers, interpreters, and assemblers are needed

   • 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 0010. It also allocates memory to variables, often resulting in an operand.
   • Interpreter
     • Before high level programming languages can be run, code is converted by an interpreter, one line at a time, into machine code, which is then executed by the CPU.
   • 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 the C programming languages by a translator.
   • Compiler
     • 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.
     • 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.
     • 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
     • Code generation
       • • Machine code is generated. • Code optimisation may be employed to make it more efficient/faster/less resource intense.

2. Types of Errors

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