High and low-level languages

High and low-level languages

1. Programmers use different programming languages to communicate with computers

   • Computer program: a list of instructions enabling a computer to perform a specific task. Computer programs can be written in high-level languages or low-level languages

2. High-level languages

   • Enable a programmer to focus on problem to be solved and requires no knowledge of the hardware and instruction set of the computer using the program. Many high-level languages are portable and can be used of different types of computers
     • Designed with programmers in mind, programs written in a high-level language are easier to: read and understand (closer to human language), write in a shorter time, debug at development stage and maintain once in use
       • Examples: C++, Delphi, Java, Pascal, Python, Visual Basic, etc

3. Low-level languages

   • Relate to specific architecture and hardware of a particular type of computer. Low-level languages can refer to machine code (binary instructions a computer can understand) or an assembly language that needs to be translated into machine code
     • Assembly languages
       • Can: make use of special hardware, make use of special machine-dependent instructions, write code that doesn't take up much space in primary memory and write code that performs a task very quickly
       • LDA: loads value of variable into accumulator
         • ADD: adds value of another variable to value stored in accumulator
           • STO: replaces value of variable by value stored in accumulator
   • Machine code
     • Programmers don't usually write in machine code as it's difficult to understand and can be complicated to manage data manipulation and storage

4. Translators

   • A program can be translated into binary before a computer can use it; this is done by a utility program called a translator
   • Interpreters
     • Computer program that reads a statement from a program written in a high-level language, performs the action specified and then does the same with the next statement and so on
       • No executable file of machine code produced, and one high-level language program statement may require several machine code instructions to be executed
         • Interpreted programs can't be used without interpreter, and an interpreter is often used when developing programs
   • Assemblers
     • Translates a program written in a low-level language into machine code
       • Executable file produced
         • One low-level language statement usually translated into one machine code instruction
           • Assembled programs can be used without assembler and an assembled program is typically distributed for general use
   • Compilers
     • Translates a program written in a high-level language into machine code
       • Executable file of machine code is produced
         • One high-level language statement can be translated into several machine code instructions
           • Compiled programs used without compilers, compiled programs are generally distributed for general use

5. Errors

   • Syntax errors
     • When a program is being compiled, if any syntax errors are found, no translated program is produced. Programmer corrects these errors and recompiles the program
       • When a program is being interpreted, the interpreter performs the actions specified by each statement until a syntax error is found. The programmer is the alerted to the place in the program where the error was found. The error is corrected by the programmer and the interpretation continues until the next error is found or the task is completed
   • Syntax error: error where program statement doesn't obey rules of programming language
     • Logic error: program doesn't do what programmer wanted it to do
   • Logic errors
     • Can be found by tracing what program does and using test data with expected results
   • IDE (Integrated/Interactive Development Environment): Used for program development, contains an editor with an interpreter and/or compiler together with debugging tools, which can improve speed of program development