Computer Programming - Keywords

So far, we have covered two important concepts called variables and their data types. We discussed how to use int, long, and float to specify different data types. We also learnt how to name the variables to store different values.

Though this chapter is not required separately because reserved keywords are a part of basic programming syntax, we kept it separate to explain it right after data types and variables to make it easy to understand.
Like int, long, and float, there are many other keywords supported by C programming language which we will use for different purpose. Different programming languages provide different set of reserved keywords, but there is one important & common rule in all the programming languages that we cannot use a reserved keyword to name our variables, which means we cannot name our variable like int or float rather these keywords can only be used to specify a variable data type.
For example, if you will try to use any reserved keyword for the purpose of variable name, then you will get a syntax error.

#include <stdio.h>

main() {

   int float;
   
   float = 10;
   
   printf( "Value of float = %d\n", float);
}

When you compile the above program, it produces the following error −

main.c: In function 'main':
main.c:5:8: error: two or more data types in declaration specifiers
    int float;
......

Let's now give a proper name to our integer variable, then the above program should compile and execute successfully −

#include <stdio.h>

main() {
   int count;

   count = 10;

   printf( "Value of count = %d\n", count);
}

C Programming Reserved Keywords

Here is a table having almost all the keywords supported by C Programming language −

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

Java Programming Reserved Keywords

Here is a table having almost all the keywords supported by Java Programming language −

abstract	assert	boolean	break
byte	case	catch	char
class	const	continue	default
do	double	else	enum
extends	final	finally	float
for	goto	if	implements
import	instanceof	int	interface
long	native	new	package
private	protected	public	return
short	static	strictfp	super
switch	synchronized	this	throw
throws	transient	try	void
volatile	while

Python Programming Reserved Keywords

Here is a table having almost all the keywords supported by Python Programming language −

and	exec	not
assert	finally	or
break	for	pass
class	from	print
continue	global	raise
def	if	return
del	import	try
elif	in	while
else	is	with
except	lambda	yield

We know you cannot memorize all these keywords, but we have listed them down for your reference purpose and to explain the concept of reserved keywords. So just be careful while giving a name to your variable, you should not use any reserved keyword for that programming language.