What is a compiler?
A compiler is a computer program (or set of programs) that transforms source code written in a computer language (the source language) into another computer language (the target language, often having a binary form known as object code). The most common reason for wanting to transform source code is to create an executable program.
The name "compiler" is primarily used for programs that translate source code from a high-level programming language to a lower level language (e.g., assembly language or machine code). A program that translates from a low level language to a higher level one is a decompiler. A program that translates between high-level languages is usually called a language translator, source to source translator, or language converter. A language rewriter is usually a program that translates the form of expressions without a change of language.
A compiler is likely to perform many or all of the following operations: lexical analysis, preprocessing, parsing, semantic analysis, code generation, and code optimization.
Program faults caused by incorrect compiler behavior can be very difficult to track down and work around and compiler implementors invest a lot of time ensuring the correctness of their software.
The term compiler-compiler is sometimes used to refer to a parser generator, a tool often used to help create the lexer and parser.
Reserved Words
Reserved Words
The identifiers listed below are reserved C keywords. You shouldn't use them for any other purpose in a C program. They are allowed, of course, within double quotation marks.
Reserved C keywords:
| Keyword | Description |
| asm | Keyword that denotes inline assembly language code. |
| auto | The default storage class. |
| break | Command that exits for, while, switch, and do...while statements unconditionally. |
| case | Command used within the switch statement. |
| char | The simplest C data type. |
| const | Data modifier that prevents a variable from being changed. See volatile. |
| continue | Command that resets a for, while, or do...while statement to the next iteration. |
| default | Command used within the switch statement to catch any instances not specified with a case statement. |
| do | Looping command used in conjunction with the while statement. The loop will always execute at least once. |
| double | Data type that can hold double-precision floating-point values. |
| else | Statement signaling alternative statements to be executed when an if statement evaluates to FALSE. |
| enum | Data type that allows variables to be declared that accept only certain values. |
| extern | Data modifier indicating that a variable will be declared in another area of the program. |
| float | Data type used for floating-point numbers. |
| for | Looping command that contains initialization, incrementation, and conditional sections. |
| goto | Command that causes a jump to a predefined label. |
| if | Command used to change program flow based on a TRUE/FALSE decision. |
| int | Data type used to hold integer values. |
| long | Data type used to hold larger integer values than int. |
| register | Storage modifier that specifies that a variable should be stored in a register if possible. |
| return | Command that causes program flow to exit from the current function and return to the calling function. It can also be used to return a single value. |
| short | Data type used to hold integers. It isn't commonly used, and it's the same size as an int on most computers. |
| signed | Modifier used to signify that a variable can have both positive and negative values. See unsigned. |
| sizeof | Operator that returns the size of the item in bytes. |
| static | Modifier used to signify that the compiler should retain the variable's value. |
| struct | Keyword used to combine C variables of any data type into a group. |
| switch | Command used to change program flow in a multitude of directions. Used in conjunction with the case statement. |
| typedef | Modifier used to create new names for existing variable and function types. |
| union | Keyword used to allow multiple variables to share the same memory space. |
| unsigned | Modifier used to signify that a variable will contain only positive values. See signed. |
| void | Keyword used to signify either that a function doesn't return anything or that a pointer being used is considered generic or able to point to any data type. |
| volatile | Modifier that signifies that a variable can be changed. See const. |
| while | Looping statement that executes a section of code as long as a condition remains TRUE. |