Keywords
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 default, for example, as the name of a variable. An attempt to do so will result in a compilation error.
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.
Data types Qualifiers User-defined Storage Classes Loop Others
int signed typedef auto for const
char unsigned enum extern while volatile
float short register do sizeof
double long static
Decision Jump Derived function
if goto struct void
else continue union return
switch break
case
default
Restrictions apply to keywords
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
Qualifier Keywords
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
Loop Control Structure Keywords
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
User-defined type Keywords
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
Jumping Control Keywords
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 Class Keywords
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
Review Questions
Part - A
1. Define Keyword.
2. List any four key words of C language.
3. What are keywords? Give examples.
4. What are the restrictions apply for keywords?
5. List any four keywords (Reserved words) of C language
Part - B
1. Write short notes on: keywords (Reserved words) in C
2. State the meaning of the following keywords in C: auto, double, int, long
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 default, for example, as the name of a variable. An attempt to do so will result in a compilation error.
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.
- 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.
Data types Qualifiers User-defined Storage Classes Loop Others
int signed typedef auto for const
char unsigned enum extern while volatile
float short register do sizeof
double long static
Decision Jump Derived function
if goto struct void
else continue union return
switch break
case
default
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.
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
Qualifier Keywords
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
Loop Control Structure Keywords
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
User-defined type Keywords
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
Jumping Control Keywords
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 Class Keywords
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
Review Questions
Part - A
1. Define Keyword.
2. List any four key words of C language.
3. What are keywords? Give examples.
4. What are the restrictions apply for keywords?
5. List any four keywords (Reserved words) of C language
Part - B
1. Write short notes on: keywords (Reserved words) in C
2. State the meaning of the following keywords in C: auto, double, int, long
