Keywords

C keeps a small set of keywords for its own use. These keywords cannot be used as identifiers in the program — a common restriction with modern languages.

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

Identifier

"Identifiers" or "symbols" are the names you supply for variables, types, functions, and labels in your program. Identifier names must differ in spelling and case from any keywords. You cannot use keywords as identifiers; they are reserved for special use.

Constants

A "constant" is a number, character, or character string that can be used as a value in a program. Use constants to represent floating-point, integer, enumeration, or character values that cannot be modified.

constant:

  • floating-point-constant
  • integer-constant
  • enumeration-constant
  • character-constant

Variables

"Variables" are simply storage locations for data. You can place data into them and retrieve their content.

For example:

int count;
char key;
char lastname[30];

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