What is programming? What are computer languages and how have they evolved? What is the basic process of programming, including the tools involved?

What is programming? What are computer languages and how have they evolved? What is the basic process of programming, including the tools involved?

A step-by-step set of instructions to accomplish a task. Example: Make KoolAid - Fill jug with water - Add KoolAid mix - Stir - Pour from jug into cups

A step-by-step set of instructions to accomplish a task expressed in a Computer Language

Machine Language - Consists of binary codes for very simplistic commands Ex: 1001 (move), 1100 (add) - Codes differ by CPU model - Is the only language a CPU can follow - Using ML Requires detailed knowledge of the CPU/hardware.

Machine Language ENIAC being programmed Univ of Penn, 1940 s (photo: U.S. Army)

Assembly Language - Consists of text codes for very simplistic commands Ex: ADD, SUB, MOVE - Codes differ by CPU model - 1-to-1 translation to Machine Language - Using Assembly requires detailed knowledge of the CPU/hardware

High Level Language - Consists of text codes for more complex expressions - Codes standardized across CPU models - 1-to-Many translation to Machine Language - Does not require detailed knowledge of the CPU/hardware.

ML vs ASSM vs HLL Assembler: Machine Lang: MOV @065 to CPU:R1 10010001 01000001 MOV @066 to CPU:R2 10010010 01000010 ADD 01010000 MOV CPU:REG3 to @067 10100010 01000011 High Level Language: x = a + b

Early High Level Languages Fortran (FORMula TRANSlation) - by IBM, 1950 s - Number cruncher for mathematicians, scientists and engineers. - Ex: A = 3.1415926 * R * R; - Very poor at manipulating pretty output and large volumes of data.

Early High Level Languages COBOL (COmmon Business Oriented Language) - by committee, funded by DoD, 1960 - For business/management apps: does pretty and handles large volumes of data easily. - Very English-Like. Ex: ADD SUBTOTAL TO TAX GIVING TOTAL.

High Level Languages - by Dennis Ritchie (AT&T), 1972 - Combines ease-of-use of a HLL with the power of Assembly - Used to write efficient systems software (Unix Operating System) C

Efficiency Accomplishing a task using the least amount of resources. In Programming, resources are: - Time (number of instructions executed) - Space (amount of memory required)

High Level Languages C++ - By Bjarne Stroustrup (AT&T), 1983 - Enhancement of C: major items: - Object-Oriented Programming - Extensibility: programmers can add new features to the language itself. Today: one of the most common languages.

Tools, Files and Errors

Software Tools Editor used to write the program in a HLL. Compiler translates program in a HLL into Machine (or other low level) Language Linker combines Object Files into an Executable. Loader copies an Executable into memory and starts program execution.

Software Tools Integrated Development Environment (IDE) Combines the editor, compiler, linker, loader and often other helpful tools into one programming tool. Example: Microsoft Visual Studio IDE

Files Source a text file containing a program written in a HLL Object part of a program translated in Machine Language Executable a complete program in Machine Language

Errors Syntax (aka Compiler) found in the Source, these are violations of the rules for writing programs in the HLL. Link the linker is unable to link the object files into an executable. Typical errors indicate something is missing or the parts (objects) do not fit together as expected.

Errors Load the loader is unable to copy the executable into memory and start execution. Typical errors include not enough memory or not a trusted program (virus protection). Run-Time occurs during execution. Typical errors include division by 0, file not found, memory access violation. Execution halts when a RTE occurs; normally called a program crash and may not have an error message.

Errors Logic (Semantic) when there is no error from the perspective of the computer, but rather the program does something unexpected by the user. Example: The program prints: The area of a square with a length of 3m is 6m 2

Errors Bug informal name for a Logic (or Run-Time) Error

- Programming is writing instructions for a computer to follow. - Various languages have been invented over the years to assist programmers. - While variations exist, there is a basic process for writing code in a HLL and translating it into ML, including use of a basic set of tools.

Term Algorithm Program Machine Language Assembly Language Definition A step-by-step set of instructions to accomplish a task A step-by-step set of instructions to accomplish a task expressed in a computer language. Binary computer language that differs by CPU model the only language a computer can follow. Language made up of simple text codes for simplistic instructions. It differs by CPU model and has a 1-to-1 translation of commands into Machine Language. High Level Language Language made up of more complex and human-language-like codes with a 1- to-many translation of commands into Machine Language. FORTRAN COBOL C Early language used to solve mathematical/scientific/engineering problems. Early language used for business data processing. Language combining the functionality of a HLL with that of Asssembly, used to write Systems Software.

Term C++ Extensibility Editor Compiler Linker Loader Source File Object File Executable File Definition An enhancement of the C language providing support for Object-Oriented Programming and language Extensibility. The ability of a programmer to extend an existing language with new features. Software tool that allows a programmer to write a program in a HLL. Software tool that translates a program in a HLL into Machine Language. Software tool that combines Object Files into a single Executable. Software tool that copies an Executable into memory and initiates program execution. Text file that contains a program written in a HLL. File that contains instructions in Machine Language, but is not a complete program. File that contains instructions in Machine Language that is a complete program.

Term Syntax Error Compiler Error Link Error Load Error Run-Time Error Logic Error Semantic Error Bug Definition Violation of a HLL rule in a Source File, discovered by the Compiler (same as Syntax Error) Error meaning the Linker is unable to combine Object Files into an Executable Error meaning the Loader is unable to copy an Executable into memory and initiate program execution. Error that occurs while a program is executing, causing the program to halt. Unexpected output/behavior of a program when there is no other type of error. (same as Logic Error) Informal word meaning Logic (or Run-Time) Error