In C programming language, a constant is an identifier that contains a specific value The value cannot be altered during normal c program execution as the value is constant.
Example
const float PI = 3.1415927; // (Pi is a constant)

for(int i=0;i<10,i++) // i is a variable

Floating-point constants

Floating point constants in C programming are the type of numeric constants that can either take decimal points or exponent form.
Example:
-2.0
0.0000234
-0.22E-5

Integer constants

Integer constants in C language are the type of numeric constants (constants associated with numbers) that do not have any fractional part or exponential part.

Three types of integer constants are available in the C programming language:

Decimal constant (base 10)
E.g. Decimal numbers: 0 1 2 3 4 5 6 7 8 9
Octal constant (base 8)
E.g. Octal numbers: 0 1 2 3 4 5 6 7
Hexadecimal constant (base 16)
E.g. Hexadecimal numbers: 0 1 2 3 4 5 6 7 8 9 A B C D E F.

Character constants

Character constants in C language are the type of constant which use single quotations around characters. For example: ‘l’, o’, ‘v’, ‘e’ etc.

Variables:

An identifier that holds the value that can be altered during normal program execution is called a variable. Variables can be visualized as memory location in the computer’s memory to store data. In other words, Variable names are just the symbolic representation of a memory location.

In C programming following basic variable types are available:

char: This is an integer type. Consume 1 byte of memory location
int: Contains decimal point free integer value. Consume 2 bytes of memory
float: Single precision floating point value. Consume 4 bytes of memory
double: Double precision floating point value. Consume 8 bytes of memory
void: Represents the absence of type.

Example

#include<stdio.h>

#include<conio.h>

void main()

{

int a=2;

float b=6.78;

char c=’x’;

double d=456.678;

clrscr();

printf(“integer=%d”,a);

printf(“\nfloat=%lf”,b);

printf(“\nchar=%c”,c);

printf(“\ndouble=%lf”,d);

getch();

}

Example

#include<stdio.h>

main()

{

int i;

float f;

char c;

clrscr();

printf(“size of i= %d”,sizeof (i));

printf(“\nsize of f= %d”, sizeof (f));

printf(“\nsize of c= %d”,sizeof (c));

getch();

}

The C programming language also gives support for two important kinds of variables that could be used for the dynamic allocation of memory.

Static variable:

static int shared = 3; //shared is of static type variable
A static variable is defined outside all blocks and has static. Always declared outside of the main block.

global variable:

global variable in C language is a type of variable that has global scope, In other words, a global variable is accessible throughout the program, unless the programmer hides it.

#include <stdio.h>
static int shared = 3; //note declaration of variable just after the library
main()
{
}

Example

#include<stdio.h>

#include<string.h>

void main()

{

int i;

static char name[7]={‘X’,’c’,’n’,’o’,’t’,’e’,’s’};

clrscr();

printf(“\n elements of the array\n”);

for(i=0;i<=6;i++)

printf(“name[%d]=%c\n”,i,name[i]);

getch();

}