Keywords in C Programming Language: A Comprehensive Guide

Rumman Ansari   Software Engineer   2024-07-04 04:56:42   49088  Share
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C programs are constructed from a set of reserved words which provide control and from libraries which perform special functions. The basic instructions are built up using a reserved set of words, such as main, for, if, while, default, double, extern, for, and int, etc., C demands that they are used only for giving commands or making statements. You cannot use a default, for example, as the name of a variable. An attempt to do so will result in a compilation error.



Restrictions apply to keywords

  • Keywords are the words whose meaning has already been explained to the C compiler and their meanings cannot be changed.
  • Keywords can be used only for their intended purpose.
  • Keywords cannot be used as user-defined variables.
  • All keywords must be written in lowercase.

Keywords have standard, predefined meanings in C. These keywords can be used only for their intended purpose; they cannot be used as programmer-defined identifiers. Keywords are an essential part of a language definition. They implement specific features of the language. Every C word is classified as either a keyword or an identifier. A keyword is a sequence of characters that the C compiler readily accepts and recognizes while being used in a program. Note that the keywords are all lowercase. Since uppercase and lowercase characters are not equivalent, it is possible to utilize an uppercase keyword as an identifier.


32 Keywords in C Programming Language

auto double int struct
break else long switch
case enum register typedef
char extern return union
const float short unsigned
continue for signed void
default goto sizeof volatile
do if static while

Keyword Types

Keyword Types Keywords
Data types

int

char

float

double

Qualifiers

signed

unsigned

short

long

User-defined

typedef

Enum

Storage Classes

auto

register

static

extern

Loop

For

While

Do

Decision

if

else

switch

case

default

Jump

Break

continue

Goto

Derived

struct

union

function

void

return

Others

const

volatile

sizeof


Data types

int Specifies the integer type of value a variable will hold
char Specifies the character type of value a variable will hold
float Specifies the single-precision floating-point of value a variable will hold
double Specifies the double-precision floating-point type of value a variable will

Qualifiers

signed Specifies a variable can hold positive and negative integer type of data
unsigned Specifies a variable can hold only the positive integer type of data
short Specifies a variable can hold fairly small integer type of data
long Specifies a variable can hold fairly large integer type of data

User-defined

typedef Used to define a new name for an existing data type
Enum Gives an opportunity to invent own data type and define what values the variable of this data type can take

Loop

For Loop is used when the number of passes is known in advance
While Loop is used when the number of passes is not known in advance
Do Loop is used to handle menu-driven programs

Decision

Jump

Break Used to force immediate termination of a loop, bypassing the conditional expression and any remaining code in the body of the loop


continue Used to take the control to the beginning of the loop bypassing the statements inside the loop
Goto Used to take the control to required place in the program

Storage Classes

Storage Classes Storage Default initial value Scope Life

auto

Memory An unpredictable value Local Till the control remains within the block
register CPU registers Garbage value Local Till the control remains within the block
static Memory Zero Local Value of the variable persists between different function calls
extern Memory Zero Global Till the program's execution doesn't come to an end

Remember: Some Important points

  • The keywords are also called ‘Reserved words’.
  • Keywords are the words whose meaning has already been explained to the C compiler and their meanings cannot be changed.
  • Keywords serve as basic building blocks for program statements.
  • Keywords can be used only for their intended purpose.
  • Keywords cannot be used as user-defined variables.
  • All keywords must be written in lowercase.
  • 32 keywords available in C.