introduction computer programming languages
- 1. COMPUTER PRESENTATION PRESENTED BY ASHIQUE ALI BAKHAT ALI MAHEEN MUNEER NOOR JAAN
- 2. Outline of Topics • Hardware/Software interface – Layers of the Machine – Kinds of Software • Computer Languages • Syntax, Semantics, Grammars • What happens to your program? – Compilation, Linking, Execution – Program errors • Compilation vs. Interpretation etc.
- 3. Software Categories • System SW –Programs written for computer systems • Compilers, operating systems, … • Application SW –Programs written for computer users • Word-processors, spreadsheets, & other application packages
- 4. A Layered View of the Computer Machine with all its hardware System Software Compilers, Interpreters,Preprocessors, etc. Operating System, Device Drivers Application Programs Word-Processors, Spreadsheets, Database Software, IDEs, etc…
- 5. Operating System (OS) Provides several essential services: – Loading & running application programs – Allocating memory & processor time – Providing input & output facilities – Managing files of information
- 6. Programs • Programs are written in programming languages – PL = programming language – Pieces of the same program can be written in different PLs • Languages closer to the machine can be more efficient • As long as they agree on how to communicate • A PL is – A special purpose and limited language – A set of rules and symbols used to construct a computer program – A language used to interact with the computer
- 7. Computer Languages – Machine Language • Uses binary code • Machine-dependent • Not portable • Assembly Language – Uses mnemonics – Machine-dependent – Not usually portable • High-Level Language (HLL) – Uses English-like language – Machine independent – Portable (but must be compiled for different platforms) – Examples: Pascal, C, C++, Java, Fortran, . . .
- 8. Machine Language • The representation of a computer program which is actually read and understood by the computer. – A program in machine code consists of a sequence of machine instructions. • Instructions: – Machine instructions are in binary code – Instructions specify operations and memory cells involved in the operation Example: Operation Address 0010 0000 0000 0100 0100 0000 0000 0101 0011 0000 0000 0110
- 9. Assembly Language • A symbolic representation of the machine language of a specific processor. • Is converted to machine code by an assembler. • Usually, each line of assembly code produces one machine instruction (One-to-one correspondence). • Programming in assembly language is slow and error- prone but is more efficient in terms of hardware performance. • Mnemonic representation of the instructions and data • Example: Load Price Add Tax Store Cost
- 10. High-level language • A programming language which use statements consisting of English-like keywords such as "FOR", "PRINT" or “IF“, ... etc. • Each statement corresponds to several machine language instructions (one-to-many correspondence). • Much easier to program than in assembly language. • Data are referenced using descriptive names • Operations can be described using familiar symbols • Example: Cost := Price + Tax
- 11. Syntax & Semantics • Syntax: – The structure of strings in some language. A language's syntax is described by a grammar. – Examples: • Binary number <binary_number> = <bit> | <bit> <binary_number> <bit> = 0 | 1 • Identifier <identifier> = <letter> {<letter> | <digit> } <letter> = a | b | . . . | z <digit = 0 | 1 | . . . | 9 • Semantics: – The meaning of the language
- 12. Syntax & Grammars • Syntax descriptions for a PL are themselves written in a formal language. – E.g. Backus-Naur Form (BNF) • The formal language is not a PL but it can be implemented by a compiler to enforce grammar restrictions. • Some PLs look more like grammar descriptions than like instructions.
- 13. Compilers & Programs • Compiler – A program that converts another program from some source language (or high-level programming language / HLL) to machine language (object code). – Some compilers output assembly language which is then converted to machine language by a separate assembler. – Is distinguished from an assembler by the fact that each input statement, in general, correspond to more than one machine instruction.
- 14. Compilation into Assembly L Compiler Assembler Source Program Assembly Language Assembly Language Machine Language
- 15. Compilers & Programs • Source program – The form in which a computer program, written in some formal programming language, is written by the programmer. – Can be compiled automatically into object code or machine code or executed by an interpreter. – Pascal source programs have extension ‘.pas’
- 16. Compilers & Programs • Object program – Output from the compiler – Equivalent machine language translation of the source program – Files usually have extension ‘.obj’ • Executable program – Output from linker/loader – Machine language program linked with necessary libraries & other files – Files usually have extension ‘.exe’
- 17. What is a Linker? • A program that pulls other programs together so that they can run. • Most programs are very large and consist of several modules. • Even small programs use existing code provided by the programming environment called libraries. • The linker pulls everything together, makes sure that references to other parts of the program (code) are resolved.
- 18. Running Programs Memory Input Data Program Output Machine language program (executable file) Data entered during execution Computed results C P U • Steps that the computer goes through to run a program:
- 19. Program Execution • Steps taken by the CPU to run a program (instructions are in machine language): 1. Fetch an instruction 2. Decode (interpret) the instruction 3. Retrieve data, if needed 4. Execute (perform) actual processing 5. Store the results, if needed
- 20. Program Errors • Syntax Errors: – Errors in grammar of the language • Runtime error: – When there are no syntax errors, but the program can’t complete execution • Divide by zero • Invalid input data • Logical errors: – The program completes execution, but delivers incorrect results – Incorrect usage of parentheses
- 21. Compilation Compiler Target Program Source Program Target Program Input Output • Compiler translates source into target (a machine language program) • Compiler goes away at execution time • Compiler is itself a machine language program, presumably created by compiling some other high-level program • Machine language, when written in a format understood by the OS is object code
- 22. Interpretation Interpreter Source Program Input Output • The interpreter stays around during execution • It reads and executes statements one at a time
- 23. Compilation vs. Interpretation • Compilation: – Syntax errors caught before running the program – Better performance – Decisions made once, at compile time • Interpretation: – Better diagnostics (error messages) – More flexibility – Supports late binding (delaying decisions about program implementation until runtime) • Can better cope with PLs where type and size of variables depend on input – Supports creation/modification of program code on the fly (e.g. Lisp, Prolog)