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"C++ is a write-only language; one can write programs in C++, but I can't read any of them"
—Programmer joke

Computers, for the most part, are dumb. If you were to take computer hardware that was freshly built off the assembly line, put the components together into a fully assembled device, and tried to turn it on, it wouldn't do anything useful (if anything at all). Yes, Microsoft Windows and macOS don't magically appear in the computer right from the factory. But if you give them something to do, they'll be able to do it really fast! But how do you tell a machine what to do? Here comes the programming language. As the name implies, it's the language you use to program the computer to do what you want.

While there are other languages in computer science, the defining characteristic of a programming language is that it's used to implement algorithms. Where it does this provides further distinction such as higher-level scripting languages. One type of computer language that's not a programming one is are markup languages, which are limited in scope to defining how something should look or at the very least, how data is organized. They may provide hints on how the data should be interpreted, but they cannot be used for computation or interfacing with the hardware or other software.

Concepts

A programming language has four basic elements to it:
  • Symbols to hold data.
  • Operators that modify the data.
  • Conditional statements that control the flow of the program.
  • The ability to jump around in the program at will.

Programs are written into source files, which can be compiled or assembled for later execution, or interpreted for execution right away. If there's something immediately wrong with the source file, the compiler, assembler, or interpreter will complain until it's fixed.

It should also be noted that a computer is more or less a Literal Genie. It's very, very rare a computer makes a mistake because it actually made a mistake. It "makes mistakes" because of how the program was written, which is entirely up to the human who wrote the code. However, the way someone writes code can make knowing how the program is supposed to function either easier or harder, so there's also an artistic side to programming.

Instruction Set Architecture (ISA)

Originally computers when they were first built were an array of logic gates that had to be hand-wired for the operations needed. As parts of computers evolved from hand-wired logic gate circuits to full on integrated circuits, a standard way of telling the chip what to do had to be made. Especially since now they could be mass produced. This is where the Instruction Set Architecture, or ISA, comes in and where the first step of building a program in modern computers starts.

The ISA in simple terms provides the interface for how the software talks with the hardware, with the software acting like the hand-wiring that used to be done. So if the ISA says feeding the binary sequence "1011111011101111" to the hardware invokes a move operation, then the software feeding the same binary sequence should do the same. There are several philosophies on how to design and implement ISAs, which is explained in Central Processing Unit. ISAs is what separates compatibility between one CPU with another.

Low-Level Languages

At its heart, a computer is simply a giant calculator that computes arithmetic billions of times per second. All of its constituent parts, from memory to modem to monitor to mouse, has an alphanumerical address associated with it. The computer uses these addresses to route data throughout itself. Hence, the earliest computer languages evolved to reflect how computers fundamentally worked. An extraordinarily simple instruction might be "Take the number stored at memory address X and subtract it from the number stored at memory address Y, then send it to the printer located at hardware address Z". Low level languages use hardware-specific instructions to talk directly to the computer this way.

A programmer can write a low-level source code in two ways:

  • Machine code: This is the most basic representation of software code. This is literally writing the 0's and 1's, or, more commonly, their hexadecimal equivalents. There's usually two portions to a machine code: the operation code (opcode), which is the instruction, and the operand(s), which is the memory location of the datum (e.g., a register or a memory address), if not the literal value to be acted upon. Computers until The '50s had to be programmed like this.
  • Assembly code: The next step in the language development introduced in The '50s. Opcodes and some special operands are now given more human-readable mnemonics, but often kept to very abbreviated words. In addition, and probably the most important addition, is that memory address can now be given labels, getting rid of the tedious job of keeping track of where one was in memory. Assembly code is machine-specific, and one cannot assume one mnemonic means the same exact operation in another machine. Because of this, porting an assembly language program to a different hardware platform usually means rewriting it completely. For instance, the CPUs in PCs and smartphones use two different assembly language instruction sets (x86 for the former, and ARM for the latter) so assembly code written for one won't work on the other.

The primary reason for using low-level languages is for maximum performance and maximum flexibility. The code that's written is directly talking to hardware and the programmer has full access (barring specific security features) to the hardware. The trade-off is that it's very easy to write code that breaks the system in software and a lack of portability. Another reason may be, especially for older or simpler systems, assembly language is easier to work with. Especially when running something like a C program, which has some overhead in setting up the system in order to run it which can eat into program space. note 

It's unusual these days to write assembly code by hand, because compilers have gotten so good at optimizing slightly higher-level languages like C. So languages are sometimes termed "low-level" because they give you a lot of control over how the assembly code turns out. In addition, many modern compilers actually allow programmers to create assembler "inserts" in the high-level source code. Some languages (such as Forth) are "multi-level" and allow both low-level and high-level coding to be done in the same syntax, and sometimes the same program.

High-Level Languages

High-level languages build on top of assembly languages by providing more human-readable ways of writing a program. For example, you could write "x = 2" instead of "MOV x, 2"; or "for(5: Array)" instead of manually looping through instructions. However, this sacrifices performance and, depending on the language, flexibility because the computer must parse the instructions and translate them into machine code. In addition, the language is typically computer agnostic, so the part that translates the code may not be able to find a 1:1 operation and has to find a way to emulate it or provide an output that makes sense.

More abstracted high-level languages go further, replacing, say, "x = 2" with "x is 2". Complex languages are written in earlier ones, "standing on the shoulders of giants"; a compiler is essentially a text parser that goes through source code for a given language and translates it into whatever lower-level language the compiler was written in. Later versions commonly use the process known as "bootstrapping", meaning that the compiler is written in the same language it compiles — and itself compiled by a previous version. Along with readability, high-level languages also allow for "portability" as long as a compiler or interpreter exists for the platform.

An important distinction with high-level languages is their intended target for what kind of programs they'll be used to program. Programs intended to talk and manipulate hardware directly are dubbed system programs, and programming languages designed for them tend to not hide details about the intimate parts of the computer. For instance, some systems programming languages allow you to manipulate things via memory addresses directly, including modifying which address you want to pull data from or write to. Programs that primarily provide some service to the user are called applications programs. Programming languages designed for applications hide the nitty and gritty parts of a computer, allowing the programmer to worry more about the features of the program rather than the lower-level details of it. Languages designed for system programs can be used to write applications (and have been for the better part of half-a-century), but programming languages meant for applications typically can't write system programs.

Source files can be executed in three different ways:

  • Ahead-of-Time Compiling (AOT): This turns the source code into an executable that can be loaded directly into memory and run without further processing. This has the fastest execution time, but is limited by what software libraries it needs and compiler support for the CPU architecture it's meant to run on.
  • Just-in-Time Compiling (JIT): The source files are run through another program or framework that compiles some of it into executable code for the computer architecture when it's needed (hence, just-in-time). While it can be fast as AOT compiled code and can run anywhere the JIT framework is available, it consumes more resources to do so.
  • Interpreting: A program executes the source code essentially line by line. While running source code is slower and more resource intensive, the source code can be run as-is. In a lot of cases, the program can be halted and the code modified on the fly. On the other hand, it requires an interpreter to be present at the machine where the program is run. If you want to see exactly how an interpreter functions, then read this tutorial about making a basic one.

Programming can be thought of as making a recipe for a dish. For instance, making a cake:

  1. Preheat the oven to 400F
  2. Put flour, eggs, sugar and milk into a bowl.
  3. Mix the ingredients for a batter.
  4. Put the batter into a pan.
  5. Bake for 30 minutes.
  6. Take the pan out and poke it with a toothpick. Does it come out clean?
    • If not, put the pan back in the oven for five minutes and test again.
    • If so, take the pan out and leave to cool for 10 minutes.
  7. You now have delicious cake to serve!

A program equivalent could look like this:

import kitchen
import toothpick

oven.temperature = 400
ingredients = [flour, eggs, sugar, milk]
batter = mix(ingredients)
cake = pour(batter)
oven.bake(cake, 30)
toothpick.poke(cake)
while not toothpick.clean:
    oven.bake(cake, 5)
    toothpick.poke(cake)
cool(cake, 10)
serve(cake)

A quirk with different programming languages is that, like natural language, different "words" have different meanings, or no meaning at all. If you wanted to display something on your monitor, you may have to type out "Print", "Display" or even C++'s exotic sounding "cout" (for character output, and pronounced "see-out"). There are also different paradigms to how to structure code. For example, procedural programming involves breaking up tasks into subroutines to make things legible. Another one, object-oriented programming, groups variables and tasks into "objects". With so many different ways to write a program or routine, a programming language can be thought of as any natural language you may learn. Thus, it's important to practice it, if you want to get good at it.

Examples of Programming Languages

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    Historical Languages 
  • BASIC (Beginner's All-purpose Symbolic Instruction Code): A family of languages designed in 1964 to be easy to learn and use. Has undergone many permutations, and its descendants bear no obvious resemblance to it or to each other. Although it's mostly used in programmable calculators and hobbyist software today, historically, it was very common in home and school microcomputers, making its use into a trope for creators who grew up in The '70s and The '80s. Many of the programming jokes in Futurama, for instance, are in BASIC. One of its descendents is Visual Basic.
  • COBOL (Common Business-Oriented Language): Created in the late 1950s by Mark Hawes with help from the US Government, COBOL is a programming language designed for use in businesses with the goal of having one language for business applications. The aim of COBOL was to make it easy for non-computer science people of the time to work with, and part of this was to make heavy use of an English-like syntax (e.g., you can do "X IS GREATER THAN Y" rather than "X > Y", though the latter can still be used). Arguably it's the lingua franca of business and government application software, where it was reported in 1997 that 80% of all business applications in the world ran on COBOL. More recently, in 2017 it was reported that nearly 43% of banks still use COBOL software. Today, knowing COBOL is highly prized due to the original developers retiring and many organizations and businesses still using software written with it.
  • FORTRAN (Originally "FORmula TRANslation System"): The very first high-level language in existence, though some call its early incarnations little more than a symbolic assembler, as a lot of features that modern programmers now take for granted simply had not yet been invented back then. Developed by IBM's John Backus in 1954 for scientific calculations and is still used to this day for the very same goal. Recent versions are actually closer to C than to the original language.
  • Lisp: Originally LISP, as in LISt Processor. Another early language (a second one, in fact), this time at a much higher level that the industry was ready for. Created by John McCarthy in 1955 as a research tool in the abstract algebra field and later found its use in AI development. Another Long Runner, which, although not as popular per se, influenced basically all modern programming languages, especially languages like Python. Is known for several rather hard-to-bend-the-brain-around concepts like first order functions and closures, as well as for its idiosyncratic (or, as many say, nonexistent) syntax that consists entirely of parentheses. Has evolved greatly with time. Popular dialects are Common Lisp and Scheme.
  • Objective-C: Apple's (originally NeXT's) cross between C and Smalltalk. Originated in NeXTstep and was briefly offered as a programming tool for Windows in the early '90s, but didn't really take off, mainly due to performance problems: PCs of the time were a lot weaker than now, and the translators weren't up to task. It was, however, revitalized by the introduction of Mac OS X and iOS, before eventually being largely replaced by Apple's Swift.

    Popular Languages 
  • C: The most widely used language in the world, with a compiler available for nearly every modern hardware platform known to man. C was primarily designed as a systems programming language making it one the most high performant languages to use. Originally used to write the UNIX OSnote , it's since been used in Windows, Linux, and macOS, the "big three" Operating Systems. Because of its mostly bare-bones nature, you can easily shoot yourself in the foot, which is why it's often jokingly referred to as a "high-level assembler".
  • C++: Started off as an extension of C to include object-oriented programming, but grew into its own general-purpose programming language that supports a variety of paradigms. Due to its direct ancestry, C++ is (mostly) compatible with C functions and applications. However, this characteristic has lend itself to be the equivalent of a CrutchCharacter in programming and has likely given C++ a bad reputation for being overly complicated and still easily capable of allowing programmers to shoot themselves in the foot. But modern C++ has features that allows programmers to get away from the pitfalls of C and early C++ (its creator, Bjarne Stroustrup, says to write C++, not C/C++). Today it's mainly used in applications that require high performance, or as the foundation of tools that other programmers use to build applications on top of.
  • C#: Microsoft's alternative to Java, which was allegedly developed after Sun axed its licensing of Java in Microsoft's development tools. C# (Pronounced "C Sharp" like the musical note) is mainly used in Windows Universal Apps and as the primary scripting language for the Unity game engine. It runs on a set of libraries called the Common Language Infrastructure, which is the .NET Framework on Windows and Mono elsewhere, and is JIT compiled using bytecode, similar to it's alleged imitatee.
  • Java: Developed by Sun in the 90s, the idea of Java was it could be compiled into so-called "bytecode", which resembled machine code of a fictional Java computer. The bytecode started off being interpreted but later extended to be JIT-compiled for performance using a Java Virtual Machine (JVM). It got its start in web applications, but soon expanded to many platforms that could run the virtual machine. It's the language that the first version of Minecraft was written in and is the primary language that Android apps are written in, though Google has stated in 2019 that they prefer Kotlin be used instead.
  • JavaScript: Developed at a time when websites could only display text and images, JavaScript gave browsers a way to provide interactive content. Later, when browser developers started making entire frameworks for running it on its own, became used in back-end and other general purpose languages. For example, you can write apps entirely in JavaScript using the NodeJS runtime environment.
  • Lua: A scripting language commonly used in games and other applications, partially thanks to its use of the very lax MIT license. The language itself is also regarded as both fast and easy to use.
  • Perl: Practical Extend and Report Language, a.k.a. Pathetically Eclectic Rubbish Lister thanks to the degree of unreadability code written in it can be. It was originally a popular language for common gateway interfaces, or programs which connected web pages to other services. Perl is the glue language of choice for UNIX and Linux Systems.
  • PHP: PHP Hypertext Preprocessor, which for years was considered a broken, unfixable mess. This Very Wiki runs PHP (look at the .php extension in this page, assuming it hasn't yet been removed), and just around 80% of the Internet also runs on it. PHP is essentially a wrapper for C and has over 8,000 functions built in!
  • Python: An interpreted language, though usually compiled in some way for performance, designed to be readable. It's used significantly in prototyping and science related fields, notably in AI. A major change happened between versions 2.7 and 3.0, causing 2.7 to be supported for many years after 3.0 was released. Though as of 2020, only the 3.0 version is now supported.
  • Ruby: Another interpreted, though now JIT compiled, language that gained popularity among web developers thanks to its efficiency when used for rapid prototyping. It's most commonly used with the Rails framework to build dynamic webpages.
  • Rust: Developed by Mozilla in the 2000s, the aims of Rust are performance, type-safety, and concurrency. It achieves this by enforcing memory safety at compile time through the Borrow Checker. This makes sure that every data is owned by some unit of execution and once that unit of execution is done, the data simply drops from memory reducing the need for automatic memory management or the developer to keep track of it. Data can be explicitly passed around, if needed. Because of this, Rust avoids many of the bugs and concurrency issues that other languages face. Another standout feature of Rust is its compiler is extremely helpful, not only pointing out where the problem is, but what the problem is. note 
  • Swift: Developed in the early 2010s by Apple, Swift was designed to replace Objective-C by combining the best traits from it and incorporating ways to ensure safe code before it gets compiled. By the late 2010s, Swift had all but replaced Objective-C as the programming language for apps made for Apple's products.
An ordered list of the 50 most popular programming languages (updated monthly) may be found here. This measures popularity based on search engine results, so it may not line up with other definitions (e.g. there may be bias towards languages for which people currently need resources, rather than those being used for production code).

    Esoteric Languages 
Languages made mostly for fun. Some of them are for testing the limits of a programmer.

Alternative Title(s): Programming Languages

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