What is the difference between a function and a procedure

Question

Generally speaking  we all hear about the functions or procedures in programming languages  However  I just found out that I use these terms almost interchangeably  which is probably very wrong    So  my question is       What is the difference in terms of their functionality  their purpose and use    An example would be appreciated

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There s a term subroutine or subprogram which stands for a parameterized piece of code that can be called from different places   Functions and procedures are implementations of those  Usually functions return values and procedures don t return anything

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In terms of    Java  function is the block of code  which return particular value  but procedure is the block of code which return void  nothing   In C  Java both functions and procedures more often called just methods         This is a function     public DateTime GetCurrentDate                 return DateTime Now Date               This is a procedure always return void      public void LogMessage                 Console WriteLine  Just an example message

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More strictly  a function f obeys the property that f x    f y  if x   y  i e  it computes the same result each time it is called with the same argument  and thus it does not change the state of the system    Thus  rand   or print  Hello    etc  are not functions but procedures  While sqrt 2 0  should be a function  there is no observable effect or state change no matter how often one calls it and it returns always 1 41 and some

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Basic Differences  A Function must return a value but in Stored Procedures it is optional  a procedure can return 0 or n values  Functions can have only input parameters for it  whereas procedures can have input output parameters  For a Function it is mandatory to take one input parameter  but a Stored Procedure may take 0 to n input parameters  Functions can be called from a Procedure whereas Procedures cannot be called from a Function   Advanced Differences  Exceptions can be handled by try-catch blocks in a Procedure  whereas a try-catch block cannot be used in a Function  We can go for Transaction Management in a Procedure  whereas in a Function we can t   In SQL   A Procedure allows SELECT as well as DML  INSERT  UPDATE  DELETE  statements in it  whereas Function allows only SELECT statement in it  Procedures can not be utilized in a SELECT statement  whereas Functions can be embedded in a SELECT statement  Stored Procedures cannot be used in SQL statements anywhere in a WHERE  or a HAVING or a SELECT  block  whereas Functions can  Functions that return tables can be treated as another Rowset  This can be used in a JOIN block with other tables  Inline Functions can be thought of as views that take parameters and can be used in JOIN blocks and other Rowset operations

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If we re language-agnostic here  procedure usually specifies a series of acts required to reliably and idempotently achieve certain result  That is  a procedure is basically an algorithm   Functions  on the other hand  is a somewhat independent piece of code within a larger program  In other words  function is the implementation of a procedure

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In most contexts  a function returns a value  while a procedure doesn t   Both are pieces of code grouped together to do the same thing   In functional programming context  where all functions return values   a function is an abstract object    f x   1 x  g x   5  2 x 2    Here  f is the same function as g  but is a different procedure

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Example in C      function int square  int n        return n   n        procedure void display  int n        printf   The value is  d   n        Although you should note that the C Standard doesn t talk about procedures  only functions

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Procedures and functions are both subroutines the only difference between them is that a procedure returns multiple  or at least can do  values whereas a function can only return one value  this is why function notation is used in maths as usually only one value is found at one given time  although some programming languages do not follow these rules this is their true definitions

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A function returns a value and a procedure just executes commands  The name function comes from math  It is used to calculate a value based on input  A procedure is a set of commands which can be executed in order  In most programming languages  even functions can have a set of commands  Hence the difference is only returning a value  But if you like to keep a function clean   just look at functional languages   you need to make sure a function does not have a side effect

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Inside procedure we can use DML  Insert  Update Delete  statements  But Inside function we can not use DML statements   Procedure can have both input output parameters   But Function can have only input parameter   We can use Try-Catch Block in Stored Procedure  But In Function We can not use Try-Catch block   We can not use Stored Procedure in Select statement  But In Function We can use in Select statement   Stored Procedure can return 0 or n values  max 1024   But Function can return only 1 value which is mandatory   Stored Procedure can not be call from Function  But We can call function from Stored Procedure   We can use transaction in Stored Procedure  But In function we can not use transaction   We can not use Stored Procedure in Sql statement anywhere in the Where Having select section  But In function we can use   We can not join Stored Procedure  But we can  join function   for more   click here   http   dotnet-developers-cafe blogspot in 2013 08 difference-between-stored-procedure-and html

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In the context of db  Stored procedure is precompiled execution plan where as functions are not

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A function returns a value and a procedure just executes commands   The name function comes from math  It is used to calculate a value based on input   A procedure is a set of command which can be executed in order   In most programming languages  even functions can have a set of commands  Hence the difference is only in the returning a value part   But if you like to keep a function clean   just look at functional languages   you need to make sure a function does not have a side effect

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Procedures  1 Procedures are the collections of statements that defines parameterized computations  2 Procedures cannot return values   3 Procedures cannot be called from function   Functions 1 Functions structurally resemble procedures but are semantically modeled on mathematical functions  2 It can return values 3 Function can be called from procedures

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This depends on the context   In Pascal-like languages  functions and procedures are distinct entities  differing in whether they do or don t return a value  They behave differently wrt  the language syntax  eg  procedure calls form statements  you cannot use a procedure call inside an expression vs  function calls don t form statements  you must use them in other statements   Therefore  Pascal-bred programmers differentiate between those   In C-like languages  and many other contemporary languages  this distinction is gone  in statically typed languages  procedures are just functions with a funny return type  This is probably why they are used interchangeably   In functional languages  there is typically no such thing as a procedure - everything is a function

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This is a well-known old question  but I d like to share some more insights about modern programming language research and design   Basic answer  Traditionally  in the sense of structured programming  and informally  a procedure is a reusable structural construct to have  input  and to do something programmable  When something is needed to be done within a procedure  you can provide  actual  arguments to the procedure in a procedure call coded in the source code  usually in a kind of an expression   and the actions coded in the procedures body  provided in the definition of the procedure  will be executed with the substitution of the arguments into the  formal  parameters used in the body   A function is more than a procedure because return values can also be specified as the  output  in the body  Function calls are more or less same to procedure calls  except that you can also use the result of the function call  syntactically  usually as a subexpression of some other expression    Traditionally  procedure calls  rather than function calls  are used to indicate that no output must be interested  and there must be side effects to avoid the call being no-ops  hence emphasizing the imperative programming paradigm  Many traditional programming languages like Pascal provide both  procedures  and  functions  to distinguish this intentional difference of styles    To be clear  the  input  and  output  mentioned above are simplified notions based on the syntactic properties of functions  Many languages additionally support passing arguments to parameters by reference sharing  to allow users transporting information encoded in arguments during the calls  Such parameter may even be just called as  in out parameter   This feature is based on the nature of the objects being passed in the calls  which is orthogonal to the properties of the feature of procedure function    However  if the result of a function call is not needed  it can be just  at least logically  ignored  and function definitions function calls should be consistent to procedure definitions procedure calls in this way  ALGOL-like languages like C  C   and Java  all provide the feature of  function  in this fashion  by encoding the result type void as a special case of functions looking like traditional procedures  there is no need to provide the feature of  procedures  separately  This prevents some bloat in the language design   Since SICP is mentioned  it is also worth noting that in the Scheme language specified by RnRS  a procedure may or may not have to return the result of the computation  This is the union of the traditional  function   returning the result  and  procedure   returning nothing   essentially same to the  function  concept of many ALGOL-like languages  and actually sharing even more guarantees like applicative evaluations of the operands before the call   However  old-fashion differences still occur even in normative documents like SRFI-96   I don t know much about the exact reasons behind the divergence  but as I have experienced  it seems that language designers will be happier without specification bloat nowadays  That is   procedure  as a standalone feature is unnecessary  Techniques like void type is already sufficient to mark the use where side effects should be emphasized  This is also more natural to users having experiences on C-like languages  which are popular more than a few decades  Moreover  it avoids the embarrassment in cases like RnRS where  procedures  are actually  functions  in the broader sense   In theory  a function can be specified with a specified unit type as the type of the function call result to indicate that result is special  This distinguishes the traditional procedures  where the result of a call is uninterested  from others  There are different styles in the design of a language    As in RnRS  just marking the uninterested results as  unspecified  value  of unspecified type  if the language has to mention it  and it is sufficient to be ignored  Specifying the uninterested result as the value of a dedicated unit type  e g  Kernel s  inert  also works  When that type is a further a bottom type  it can be  hopefully  statically verified and prevented used as a type of expression  The void type in ALGOL-like languages is exactly an example of this technique  ISO C11 s  Noreturn is a similar but more subtle one in this kind    Further reading  As the traditional concept derived from math  there are tons of black magic most people do not bother to know  Strictly speaking  you won t be likely get the whole things clear as per your math books  CS books might not provide much help  either   With concerning of programming languages  there are several caveats    Functions in different branches of math are not always defined having same meanings  Functions in different programming paradigms may also be quite different  even sometimes the syntaxes of function call look similar   Sometimes the reasons to cause the differences are same  but sometimes they are not    It is idiomatic to model computation by mathematical functions and then implement the underlying computation in programming languages  Be careful to avoid mapping them one to one unless you know what are being talked about   Do not confuse the model with the entity be modeled    The latter is only one of the implementation to the former  There can be more than one choices  depending on the contexts  the branches of math interested  for example   In particular  it is more or less similarly absurd to treat  functions  as  mappings  or subsets of Cartesian products like to treat natural numbers as Von-Neumann encoding of ordinals  looking like a bunch of                besides some limited contexts   Mathematically  functions can be partial or total  Different programming languages have different treatment here    Some functional languages may honor totality of functions to guarantee the computation within the function calls always terminate in finite steps  However  this is essentially not Turing-complete  hence weaker computational expressiveness  and not much seen in general-purpose languages besides semantics of typechecking  which is expected to be total   If the difference between the procedures and functions is significant  should there be  total procedures   Hmm     Constructs similar to functions in calculi used to model the general computation and the semantics of the programming languages  e g  lambda abstractions in lambda calculi  can have different evaluation strategies on operands    In traditional the reductions in pure calculi as well in as evaluations of expressions in pure functional languages  there are no side effects altering the results of the computations  As a result  operands are not required to be evaluated before the body of the functions-like constructs  because the invariant to define  same results  is kept by properties like   -equivalence guaranteed by Church-Rosser property   However  many programming languages may have side effects during the evaluations of expressions  That means  strict evaluation strategies like applicative evaluation are not the same to non-strict evaluation ones like call-by-need  This is significant  because without the distinction  there is no need to distinguish function-like  i e  used with arguments  macros from  traditional  functions  But depending on the flavor of theories  this still can be an artifact  That said  in a broader sense  functional-like macros  esp  hygienic ones  are mathematical functions with some unnecessary limitations  syntactic phases   Without the limitations  it might be sane to treat  first-class  function-like macros as procedures    For readers interested in this topic  consider some modern abstractions   Procedures are usually considered out of the scope of traditional math  However  in calculi modeling the computation and programming language semantics  as well as contemporary programming language designs  there can be quite a big family of related concepts sharing the  callable  nature  Some of them are used to implement extend replace procedures functions  There are even more subtle distinctions    Here are some related keywords  subroutines  stackless stackful  coroutines  undelimited delimited  continuations    and even  unchecked  exceptions

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I object with something I keep seeing over and over in most of these answers  that what makes a function a function is that it returns a value   A function is not just any old method that returns a value   Not so  In order for a method to be a real function it must return the same value always given a specific input   An example of a method that is not a function is the random method in most languages  because although it does return a value the value is not always the same   A function therefore is more akin to a map   e g  where x - gt  x  for a one dimensional function    This is a very important distinction between regular methods and functions because when dealing with real functions the timing and the order in which they are evaluated should never matter where as this is not always the case with non functions   Here s another example of a method that is not a function but will otherwise still return a value      The following is pseudo code  g x        if  morning           g   2   x        else      g   x        return g      I further object to the notion that procedures do not return values   A procedure is just a specific way of talking about a function or method   So that means if the underlying method that your procedure defines or implements returns a value then  guess what that procedure returns a value   Take for example the following snippet from the SICP      We can immediately translate this definition into a recursive procedure     for computing Fibonacci numbers    define  fib n     cond     n 0  0              n 1  1           else     fib  - n 1                     fib  - n 2         Have you heard of recursive procedures much lately  They are talking about a recursive function  a real function  and it s returning a value and they are using the word  procedure    So what s the difference  then   Well another way of thinking of a function  besides the meaning mentioned above  is as an abstract representation of an ideal like the numeral 1  A procedure is that actual implementation of that thing   I personally think they are interchangeable    Note  if you read that chapter from the link I provide you may find that a harder concept to grasp is not the difference between a function and a procedure  but a process and a procedure   Did you know that a recursive procedure can have an iterative process    An analog for procedures are recipes   For example  suppose you have a machine called make-pies this machine takes in ingredients of  fruit  milk  flower  eggs  sugar  heat  and this machine returns a pie   A representation of this machine might look like  make-pies  fruit  milk  flower  eggs  sugar  heat         return  heat  add fruit  mix eggs flower milk        Of course that s not the only way to make a pie   In this case we can see that   A       function     is to a     machine as a    procedure    is to a     recipe as      attributes   are to      ingredients as      output       is to       product   That analogy is OK but it breaks down when you take into account that when you are dealing with a computer program everything is an abstraction   So unlike in the case of a recipe to a machine we are comparing two things that are themselves abstractions  two things that might as well be the same thing   And I hold that they are  for all intent and purposes  the same thing

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In general  a procedure is a sequence of instructions  A function can be the same  but it usually returns a result

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Function can be used within a sql statement whereas procedure cannot be used within a sql statement   Insert  Update and Create statements cannot be included in function but a procedure can have these statements   Procedure supports transactions but functions do not support transactions   Function has to return one and only one value  another can be returned by OUT variable  but procedure returns as many data sets and return values   Execution plans of both functions and procedures are cached  so the performance is same in both the cases

[function] What is the difference between a "function" and a "procedure"?

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