What is the difference between syntax and semantics in programming languages

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What is the difference between syntax and semantics in programming languages  like C  C

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Syntax is the structure or form of expressions  statements  and program units but Semantics is the meaning of those expressions  statements  and program units  Semantics follow directly from syntax   Syntax refers to the structure form of the code that a specific programming language specifies but Semantics deal with the meaning assigned to the symbols  characters and words

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Wikipedia has the answer  Read syntax  programming languages   amp  semantics  computer science  wikipages   Or think about the work of any compiler or interpreter  The first step is lexical analysis  where tokens are generated by dividing string into lexemes then parsing  which build some abstract syntax tree  which is a representation of syntax   The next steps involves transforming or evaluating these AST  semantics    Also  observe that if you defined a variant of C where every keyword was transformed into its French equivalent  so if becoming si  do becoming faire  else becoming sinon etc etc     you would definitely change the syntax of your language  but you won t change much the semantics  programming in that French-C won t be easier

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The syntax of a programming language is the form of its expressions  statements  and program units  Its semantics is the meaning of those expressions  statements  and program units  For example  the syntax of a Java while statement is  while  boolean expr  statement   The semantics of this statement form is that when the current value of the Boolean expression is true  the embedded statement is executed  Then control implicitly returns to the Boolean expression to repeat the process  If the Boolean expression is false  control transfers to the statement following the while construct

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You need correct syntax to compile  You need correct semantics to make it work

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Semantics is what your code means--what you might describe in pseudo-code   Syntax is the actual structure--everything from variable names to semi-colons

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Syntax is about the structure or the grammar of the language  It answers the question  how do I construct a valid sentence  All languages  even English and other human  aka  natural   languages have grammars  that is  rules that define whether or not the sentence is properly constructed   Here are some C language syntax rules    separate statements with a semi-colon enclose the conditional expression of an IF statement inside parentheses group multiple statements into a single statement by enclosing in curly braces data types and variables must be declared before the first executable statement  this feature has been dropped in C99  C99 and latter allow mixed type declarations     Semantics is about the meaning of the sentence  It answers the questions  is this sentence valid  If so  what does the sentence mean  For example   x                        increment foo xyz  --b   amp qrs       call foo   are syntactically valid C statements  But what do they mean  Is it even valid to attempt to transform these statements into an executable sequence of instructions  These questions are at the heart of semantics   Consider the    operator in the first statement  First of all  is it even valid to attempt this    If x is a float data type  this statement has no meaning  according to the C language rules  and thus it is an error even though the statement is syntactically correct  If x is a pointer to some data type  the meaning of the statement is to  add sizeof some data type  to the value at address x and store the result into the location at address x    If x is a scalar  the meaning of the statement is  add one to the value at address x and store the result into the location at address x     Finally  note that some semantics cannot be determined at compile-time and must therefore must be evaluated at run-time  In the    operator example  if x is already at the maximum value for its data type  what happens when you try to add 1 to it  Another example  what happens if your program attempts to dereference a pointer whose value is NULL   In summary  syntax is the concept that concerns itself only whether or not the sentence is valid for the grammar of the language   Semantics is about whether or not the sentence has a valid meaning

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Understanding how the compiler sees the code  Usually  syntax and semantics analysis of the code is done in the  frontend  part of the compiler    Syntax  Compiler generates tokens for each keyword and symbols  the token contains the information- type of keyword and its location in the code  Using these tokens  an AST short for Abstract Syntax Tree  is created and analysed  What compiler actually checks here is whether the code is lexically meaningful i e  does the  sequence of keywords  comply with the language rules  As suggested in previous answers  you can see it as the grammar of the language not the sense meaning of the code   Side note  Syntax errors are reported in this phase  returns tokens with the error type to the system  Semantics  Now  the compiler will check whether your code operations  makes sense   e g  If the language supports Type Inference  sematic error will be reported if you re trying to assign a string to a float  OR declaring the same variable twice  These are errors that are  grammatically   syntaxially correct  but makes no sense during the operation  Side note  For checking whether the same variable is declared twice  compiler manages a symbol table   So  the output of these 2 frontend phases is an annotated AST with data types  and symbol table   Understanding it in a less technical way  Considering the normal language we use  here  English   e g  He go to the school  - Incorrect grammar syntax  though he wanted to convey a correct sense semantic   e g  He goes to the cold  - cold is an adjective  In English  we might say this doesn t comply with grammar  but it actually is the closest example to incorrect semantic with correct syntax I could think of

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Syntax  It is referring to grammatically structure of the language    If you are writing the c language   You have to very care to use of data types  tokens   it can be literal or symbol like  printf     It has 3 tokes   printf           In the same way  you have to very careful  how you use function  function syntax  function declaration  definition  initialization and calling of it   While semantics  It concern to logic or concept of sentence or statements  If you saying or writing something out of concept or logic  then you are semantically wrong

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He drinks rice  wrong semantic- meaningless  right syntax- grammar   Hi drink water  right semantic- has meaning  wrong syntax- grammar

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Syntax refers to the structure of a language  tracing its etymology to how things are put together   For example you might require the code to be put together by declaring a type then a name and then a semicolon  to be syntactically correct   Type token    On the other hand  the semantics is about meaning   A compiler or interpreter could complain about syntax errors  Your co-workers will complain about semantics

[syntax] What is the difference between syntax and semantics in programming languages?

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