Learn C - C Keywords

There are 32 words defined as keywords in the standard ANSI C programming language.

These keywords have predefined uses and cannot be used for any other purpose in a C program.

These keywords are used by the compiler.

Keyword	Description
auto	Defines a local variable as having a local lifetime
break	Passes control out of the programming construct
case	Branch control
char	Basic data type
const	Unmodifiable value
continue	Passes control to loop's beginning
default	Branch control
do	Do While loop
double	Floating-point data type
else	Conditional statement
enum	Defines a group of constants of type int
extern	Indicates an identifier as defined elsewhere
float	Floating-point data type
for	For loop
goto	Transfers program control unconditionally
if	Conditional statement
int	Basic data type
long	Type modifier
register	Stores the declared variable in a CPU register
return	Exits the function
short	Type modifier
signed	Type modifier
sizeof	Returns expression or type size
static	Preserves variable value after its scope ends
struct	Groups variables into a single record
switch	Branch control
typedef	Creates a new type
union	Groups variables that occupy the same storage space
unsigned	Type modifier
void	Empty data type
volatile	Allows a variable to be changed by a background routine
while	Repeats program execution while the condition is true

Example


#include <stdio.h> 
int main(void) 
{ /*  w  ww . j  av a  2 s .  com*/
   float fRevenue, fCost; 
   fRevenue = 0; 
   fCost = 0; 
   /* profit = revenue - cost */ 
   printf("\nEnter total revenue: "); 
   scanf("%f", &fRevenue); 
   printf("\nEnter total cost: "); 
   scanf("%f", &fCost); 
   printf("\nYour profit is $%.2f\n", fRevenue - fCost); 
   
   return 0;
}

The code above generates the following result.

Note

using characters as menu choices.


#include <stdio.h>  
int main(void) 
{ /*  w  ww . j av a 2  s  . c o m*/
   char cResponse = '\0'; 
   printf("\n\tAC Control Unit\n"); 
   printf("\na\tTurn the AC on\n"); 
   printf("b\tTurn the AC off\n"); 
   printf("\nEnter your selection: "); 
   scanf("%c", &cResponse); 
   if (cResponse == 'a') 
      printf("\nAC is now on\n"); 
   if (cResponse == 'b') 
      printf("\nAC is now off\n"); 
    
   return 0;
}

The code above generates the following result.