Introduction to Programming - (C Language) - Unit : 1 – VARIABLES AND CONSTANTS

 

VARIABLES AND CONSTANTS

VARIABLES:

The quantities which can be changed during the execution of program are called Variables. A variable can be considered as the name of the cell which can hold the constants. To use any variable it must be declared with its data type before the first executable statement and they can be initialized. Naming the variable is very important.

Rules for declaring variables:

1)   The variable name must be start with either alphabets or an underscore and may contain alphabets, digits, hyphen or underscore.

2)   The maximum length of a variable is 8 characters. But some compilers  can accept upto 32 characters.

3)   There must not be any blank spaces or special symbols in a variable  name except underscore symbol ( _ ).

4)   A variable name must not be a keyword.

 Ex:             valid                                         invalid

                      eno                                               emp name

                      empname                                      emp(name

                      emp-name                                     45abc

 

Useful tips in naming variables:

1.   Variables must be related to content stored in it.

2.   Length of the variable is 3-6 letters.

3.   Avoid vowels in variable names.

4.   Use underscores instead of spaces.

Ex: ttl_mrk (total marks)

Declaring & initializing C variable:

·  Variables should be declared in the C program before to use.

·  Memory space is not allocated for a variable while declaration. It happens only on variable definition.

·  Variable initialization means assigning a value to the variable.

Variable declarations

This is the process of allocating sufficient memory space for the data in term of variable.

Syntax: Datatype variable_name;

Ex: int a;

If no input values are assigned by the user than system will gives a default value called garbage value.

Garbage value

Garbage value can be any value given by system and that is no way related to correct programs. This is a disadvantage of C programming language and in C programming it can overcome using variable initialization.

S.No	Type	Syntax	Example
1	Variable declaration	data_type variable_name;	int x, y, z;  char flat, ch;
2	Variable initialization	data_type variable_name = value;	int x = 50, y = 30; char flag = ‘x’, ch=’l’;

 

 

 CONSTANTS : The unchangeable quantities are called Constants. The constants are generally two types.

1)   Character constants :

              a) Characters    Ex:  ‘a’, ‘5’, ‘+’, ‘ ‘, ...

              b) Strings           Ex:  “abc”, “435”, ‘rama”, ...

2)   Numeric Constants :

a) integers          Ex: 435, -657, 65535, -32768,...

b) Real numbers

i) Fractional form   Ex:  435.67, 345.00054, ...

ii) Exponential form  Ex:  0.02e3, 1.17e-38, ...

Constants in C

A constant is a value or variable that can't be changed in the program, for example: 10, 20, 'a', 3.4, "c programming" etc.

There are different types of constants in C programming.

List of Constants in C

Constant	Example
Decimal Constant	10, 20, 450 etc.
Real or Floating-point Constant	10.3, 20.2, 450.6 etc.
Octal Constant	021, 033, 046 etc.
Hexadecimal Constant	0x2a, 0x7b, 0xaa etc.
Character Constant	'a', 'b', 'x' etc.
String Constant	"c", "c program", "c in javatpoint" etc.

 

2 ways to define constant in C

There are two ways to define constant in C programming.

1. const keyword
2. #define preprocessor

3.      KEYWORDS: These are predefined words. There are 32 keywords in C language. These keywords can not be used as user-defined variables.

Keywords in C Programming
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

 

 

BASIC INPUT AND OUTPUT

Input Functions:

scanf(): Used to read input from the standard input (usually the keyboard) based on a specified format.

Example:

int num;

scanf("%d", &num);

 

getchar(): Reads a single character from the standard input.

Example:

char ch = getchar();

 

gets(): Reads a line of text from the standard input. (Note: gets() is generally discouraged due to security risks. It's better to use fgets() for safe input.)

Example:

 

char buffer[100];

gets(buffer);

 

Output Functions:

printf(): Used to print formatted data to the standard output (usually the console).

Example:

int num = 42;

printf("The number is: %d\n", num);

 

putchar(): Writes a single character to the standard output.

Example:

char ch = 'A';

putchar(ch);

 

puts(): Writes a string to the standard output followed by a newline character.

Example:

puts("Hello, world!");

 

Formatted Input and Output:

You can use various format specifiers with printf() and scanf() to format input and output according to your needs. Some common format specifiers include %d (for integers), %f (for floating-point numbers), %c (for characters), and %s (for strings), among others.