Keywords in C

A keyword is a reserved word. You cannot use it as a variable name, constant name etc. There are only 32 reserved words (keywords) in C language.

A list of 32 keywords in c language is given below:

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

We will learn about all the C language keywords later.

C Operators

An operator is simply a symbol that is used to perform operations. There can be many types of operations like arithmetic, logical, bitwise etc.

There are following types of operators to perform different types of operations in C language.

• Arithmetic Operators
• Relational Operators
• Shift Operators
• Logical Operators
• Bitwise Operators
• Ternary or Conditional Operators
• Assignment Operator
• Misc Operator

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Precedence of Operators in C

The precedence of operator species that which operator will be evaluated first and next. The associativity specifies the operators direction to be evaluated, it may be left to right or right to left.

Let's understand the precedence by the example given below:

1. int value=10+20*10;  

The value variable will contain 210 because * (multiplicative operator) is evaluated before + (additive operator).

The precedence and associativity of C operators is given below:

Category	Operator	Associativity
Postfix	() [] -> . ++ - -	Left to right
Unary	+ - ! ~ ++ - - (type)* & sizeof	Right to left
Multiplicative	* / %	Left to right
Additive	+ -	Left to right
Shift	<< >>	Left to right
Relational	< <= > >=	Left to right
Equality	== !=	Left to right
Bitwise AND	&	Left to right
Bitwise XOR	^	Left to right
Bitwise OR	|	Left to right
Logical AND	&&	Left to right
Logical OR	||	Left to right
Conditional	?:	Right to left
Assignment	= += -= *= /= %=>>= <<= &= ^= |=	Right to left
Comma	,	Left to right

Comments in C

Comments in C language are used to provide information about lines of code. It is widely used for documenting code. There are 2 types of comments in C language.

1. Single Line Comments
2. Multi Line Comments

Single Line Comments

Single line comments are represented by double slash \\. Let's see an example of single line comment in C.

1. #include <stdio.h>      
2. #include <conio.h>    
3. void main(){      
4. clrscr();      
5. //printing information  
6. printf("Hello C");  
7. getch();      
8. }      

Output:

Hello C

Even you can place comment after statement. For example:

1. printf("Hello C");//printing information  

Mult Line Comments

Multi line comments are represented by slash asterisk \* ... *\. It can occupy many lines of code but it can't be nested. Syntax:

1. /*  
2. code 
3. to be commented 
4. */  

Let's see an example of multi line comment in C.

1. #include <stdio.h>      
2. #include <conio.h>    
3. void main(){      
4. clrscr();      
5. /*printing 
6. information*/  
7. printf("Hello C");  
8. getch();      
9. }      

Output:

Hello C

Escape Sequence in C

An escape sequence in C language is a sequence of characters that doesn't represent itself when used inside string literal or character.

It is composed of two or more characters starting with backslash \. For example: \n represents new line.

List of Escape Sequences in C

Escape Sequence	Meaning
\a	Alarm or Beep
\b	Backspace
\f	Form Feed
\n	New Line
\r	Carriage Return
\t	Tab (Horizontal)
\v	Vertical Tab
\\	Backslash
\'	Single Quote
\"	Double Quote
\?	Question Mark
\nnn	octal number
\xhh	hexadecimal number
\0	Null

Escape Sequence Example

1. #include <stdio.h>      
2. #include <conio.h>    
3. void main(){      
4. int number=50;    
5. clrscr();      
6. printf("You\nare\nlearning\n\'c\' language\n\"Do you know C language\"");  
7. getch();      
8. }      

Output:

You
are
learning
'c' language
"Do you know C language"

Data Types in C

A data type specifies the type of data that a variable can store such as integer, floating, character etc.
There are 4 types of data types in C language.

Types	Data Types
Basic Data Type	int, char, float, double
Derived Data Type	array, pointer, structure, union
Enumeration Data Type	enum
Void Data Type	void

Basic Data Types

The basic data types are integer-based and floating-point based. C language supports both signed and unsigned literals.
The memory size of basic data types may change according to 32 or 64 bit operating system.
Let's see the basic data types. It size is given according to 32 bit OS.

Data Types	Memory Size	Range
char	1 byte	−128 to 127
signed char	1 byte	−128 to 127
unsigned char	1 byte	0 to 127
short	2 byte	−32,768 to 32,767
signed short	2 byte	−32,768 to 32,767
unsigned short	2 byte	0 to 32,767
int	2 byte	−32,768 to 32,767
signed int	2 byte	−32,768 to 32,767
unsigned int	2 byte	0 to 32,767
short int	2 byte	−32,768 to 32,767
signed short int	2 byte	−32,768 to 32,767
unsigned short int	2 byte	0 to 32,767
long int	4 byte
signed long int	4 byte
unsigned long int	4 byte
float	4 byte
double	8 byte
long double	10 byte

printf scanf in C

The printf() and scanf() functions are used for input and output in C language. Both functions are inbuilt library functions, defined in stdio.h (header file).

printf() function

The printf() function is used for output. It prints the given statement to the console.

The syntax of printf() function is given below:

1. printf("format string",argument_list);  

The format string can be %d (integer), %c (character), %s (string), %f (float) etc.

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scanf() function

The scanf() function is used for input. It reads the input data from the console.

1. scanf("format string",argument_list);  

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Program to print cube of given number

Let's see a simple example of c language that gets input from the user and prints the cube of the given number.

1. #include<stdio.h>  
2. #include<conio.h>  
3. void main(){  
4. int number;  
5. clrscr();  
6.   
7. printf("enter a number:");  
8. scanf("%d",&number);  
9.   
10. printf("cube of number is:%d ",number*number*number);  
11.   
12. getch();  
13. }  

Output

enter a number:5
cube of number is:125

The scanf("%d",&number) statement reads integer number from the console and stores the given value in number variable.

The printf("cube of number is:%d ",number*number*number) statement prints the cube of number on the console.

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Program to print sum of 2 numbers

Let's see a simple example of input and output in C language that prints addition of 2 numbers.

1. #include<stdio.h>  
2. #include<conio.h>  
3. void main(){  
4. int x=0,y=0,result=0;  
5. clrscr();  
6.   
7. printf("enter first number:");  
8. scanf("%d",&x);  
9. printf("enter second number:");  
10. scanf("%d",&y);  
11.   
12. result=x+y;  
13. printf("sum of 2 numbers:%d ",result);  
14.   
15. getch();  
16. }  

Output

enter first number:9
enter second number:9
sum of 2 numbers:18

Variables in C

A variable is a name of memory location. It is used to store data. Its value can be changed and it can be reused many times.

It is a way to represent memory location through symbol so that it can be easily identified.

Let's see the syntax to declare a variable:







type variable_list;  




The example of declaring variable is given below:







int a;  
float b;  
char c;  




Here, a, b, c are variables and int,float,char are data types.

We can also provide values while declaring the variables as given below:







int a=10,b=20;//declaring 2 variable of integer type  
float f=20.8;  
char c='A';  




There are many types of variables in c:

local variable
global variable
static variable
automatic variable
external variable



Local Variable

A variable that is declared inside the function or block is called local variable.

It must be declared at the start of the block.







void function1(){  
int x=10;//local variable  
}  




You must have to initialize the local variable before it is used.


Global Variable

A variable that is declared outside the function or block is called global variable. Any function can change the value of the global variable. It is available to all the functions.

It must be declared at the start of the block.







int value=20;//global variable  
void function1(){  
int x=10;//local variable  
}  





Static Variable

A variable that is declared with static keyword is called static variable.

It retains its value between multiple function calls.







void function1(){  
int x=10;//local variable  
static int y=10;//static variable  
x=x+1;  
y=y+1;  
printf("%d,%d",x,y);  
}  




If you call this function many times, local variable will print the same value for each function call e.g, 11,11,11 and so on. But static variable will print the incremented value in each function call e.g. 11, 12, 13 and so on.


Automatic Variable

All variables in C that is declared inside the block, are automatic variables by default. By we can explicitly declare automatic variable using auto keyword.







void main(){  
int x=10;//local variable (also automatic)  
auto int y=20;//automatic variable  
}  





External Variable

We can share a variable in multiple C source files by using external variable. To declare a external variable, you need to use extern keyword.
myfile.h







extern int x=10;//external variable (also global)  



program1.c







#include "myfile.h"  
#include <stdio.h>  
void printValue(){  
    printf("Global variable: %d", global_variable);  
}