Comparison of programming languages (basic instructions)

This article compares a large number of programming languages by tabulating their data types, their expression, statement, and declaration syntax, and some common operating-system interfaces.
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Conventions of this article

Generally, ''var'', , or is how variable names or other non-literal values to be interpreted by the reader are represented. The rest is literal code. Guillemets ( and ) enclose optional sections. indicates a necessary (whitespace) indentation.

Note that the tables are not sorted lexicographically ascending by programming-language name by default, and that some programming languages have entries in some tables but not others.

Type identifiers

Integers

* The ''standard'' constants and can be used to determine how many s and s can be usefully prefixed to and . The actual sizes of , , and are available as the constants , , and etc.
* Commonly used for characters.
* The ALGOL 68, C and C++ languages do not specify the exact width of the integer types , , , and (C99, C++11) , so they are implementation-dependent. In C and C++ , , and types are required to be at least 16, 32, and 64 bits wide, respectively, but can be more. The type is required to be at least as wide as and at most as wide as , and is typically the width of the word size on the processor of the machine (i.e. on a 32-bit machine it is often 32 bits wide; on 64-bit machines it is sometimes 64 bits wide). C99 and C++11 also define the exact-width types in the stdint.h header. See C syntax#Integral types for more information. In addition the types and are defined in relation to the address size to hold unsigned and signed integers sufficiently large to handle array indices and the difference between pointers.
* Perl 5 does not have distinct types. Integers, floating point numbers, strings, etc. are all considered "scalars".
* PHP has two arbitrary-precision libraries. The BCMath library just uses strings as datatype. The GMP library uses an internal "resource" type.
* The value of is provided by the intrinsic function.
* ALGOL 68G's runtime option can set precision for s to the required "number" significant digits. The ''standard'' constants and can be used to determine actual precision.
* COBOL allows the specification of a required precision and will automatically select an available type capable of representing the specified precision. "", for example, would require a signed variable of four decimal digits precision. If specified as a binary field, this would select a 16-bit signed type on most platforms.
* Smalltalk automatically chooses an appropriate representation for integral numbers. Typically, two representations are present, one for integers fitting the native word size minus any tag bit () and one supporting arbitrary sized integers (). Arithmetic operations support polymorphic arguments and return the result in the most appropriate compact representation.
* Ada range types are checked for boundary violations at run-time (as well as at compile-time for static expressions). Run-time boundary violations raise a "constraint error" exception. Ranges are not restricted to powers of two. Commonly predefined Integer subtypes are: Positive (range 1 .. Integer'Last) and Natural (range 0 .. Integer'Last). (8 bits), (16 bits) and (64 bits) are also commonly predefined, but not required by the Ada standard. Runtime checks can be disabled if performance is more important than integrity checks.
* Ada modulo types implement modulo arithmetic in all operations, i.e. no range violations are possible. Modulos are not restricted to powers of two.
* Commonly used for characters like Java's char.
* in PHP has the same width as type in C has on that system.
* Erlang is dynamically typed. The type identifiers are usually used to specify types of record fields and the argument and return types of functions.
* When it exceeds one word.

Floating point

* The ''standard'' constants and can be used to determine how many s and s can be usefully prefixed to and . The actual sizes of , , and are available as the constants , and etc. With the constants , and available for each type's machine epsilon.
* declarations of single precision often are not honored
* The value of is provided by the intrinsic function.
* ALGOL 68G's runtime option can set precision for s to the required "number" significant digits. The ''standard'' constants and can be used to determine actual precision.
* These IEEE floating-point types will be introduced in the next COBOL standard.
* Same size as on many implementations.
* Swift supports 80-bit extended precision floating point type, equivalent to in C languages.

Complex numbers

* The value of is provided by the intrinsic function.
* Generic type which can be instantiated with any base floating point type.

Other variable types

* specifically, strings of arbitrary length and automatically managed.
* This language represents a boolean as an integer where false is represented as a value of zero and true by a non-zero value.
* All values evaluate to either true or false. Everything in ' evaluates to true and everything in ' evaluates to false.
* This language does not have a separate character type. Characters are represented as strings of length 1.
* Enumerations in this language are algebraic types with only nullary constructors
* The value of ' is provided by the intrinsic function.

Derived types

Array

* In most expressions (except the sizeof and operators), values of array types in C are automatically converted to a pointer of its first argument. See C syntax#Arrays for further details of syntax and pointer operations.
* The C-like ''type'' x[] works in Java, however ''type''[] x is the preferred form of array declaration.
* Subranges are used to define the bounds of the array.
* JavaScript's array are a special kind of object.
* The clause in COBOL does not create a ''true'' variable length array and will always allocate the maximum size of the array.

Other types

* Only classes are supported.
* s in C++ are actually classes, but have default public visibility and ''are'' also POD objects. C++11 extended this further, to make classes act identically to POD objects in many more cases.
* pair only
* Although Perl doesn't have records, because Perl's type system allows different data types to be in an array, "hashes" (associative arrays) that don't have a variable index would effectively be the same as records.
* Enumerations in this language are algebraic types with only nullary constructors

Variable and constant declarations

* Pascal has declaration blocks. See functions.
* Types are just regular objects, so you can just assign them.
* In Perl, the "my" keyword scopes the variable into the block.
* Technically, this does not declare ''name'' to be a mutable variable—in ML, all names can only be bound once; rather, it declares ''name'' to point to a "reference" data structure, which is a simple mutable cell. The data structure can then be read and written to using the and operators, respectively.
* If no initial value is given, an invalid value is automatically assigned (which will trigger a run-time exception if it used before a valid value has been assigned). While this behaviour can be suppressed it is recommended in the interest of predictability. If no invalid value can be found for a type (for example in case of an unconstraint integer type), a valid, yet predictable value is chosen instead.
* In Rust, if no initial value is given to a or variable and it is never assigned to later, there is a
"unused variable" warning
If no value is provided for a or or variable, there is an error. There is

error for non-uppercase variables. After it is defined, a variable can only be assigned to in an block or function.

Control flow

Conditional statements

* A single instruction can be written on the same line following the colon. Multiple instructions are grouped together in a