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  C Programming Tutorials
Basics of C:
Facts about C
Why to Use C
C Program File
C Compilers

Program Structure:
Simple C Program
C Program Compilation

Basic DataTypes:
DataTypes
Modifiers
Qualifiers
Arrays

Variable Types:
Local Variable
Global Variable

Storage Classes:
auto storage class
register storage class
static storage class
extern storage class

Using Constants:
Defining Constants
The enum Data Types

Operator Types:
Arithmetic Operators
Logical Operators
Bitwise Operators
Assignment Operators
Misc Operators

Control Statements:
Branching
Looping

Input and Output:
printf() function
scanf() function

Pointing to Data:
Pointers and Arrays
Pointer Arithmetic
Pointer Arithmetic with arrays

Functions:
Using functions
Declaration and Definition

Strings:
Reading and Writing Strings
String Manipulation Function

Structured DataTypes:
Structure
Pointer to Structure

Working with Files:
Files
Basic I/O

Bits:
Bits Manipulation
Bits Field

Pre-Processors:
Pre-Processors Examples
Parameterized Macros
Macro Caveats

Useful Concepts

Built-in Library Functions:
String Manipulation Function
Memory Management Function
Buffer Manipulation
Character Functions
Error Handling Functions

Soft Skills
Communication Skills
Leadership Skills
                              .........More

 

 

  

C Programming Tutorials


Variable Types
A variable is just a named area of storage that can hold a single value (numeric or character). The C language demands that you declare the name of each variable that you are going to use and its type, or class, before you actually try to do anything with it.

The Programming language C has two main variable types

  • Local Variables

  • Global Variables

Local Variables

  • Local variables scope is confined within the block or function where it is defined. Local variables must always be defined at the top of a block.

  • When a local variable is defined - it is not initialized by the system, you must initialize it yourself.

  • When execution of the block starts the variable is available, and when the block ends the variable 'dies'.

Check following example's output

 main()
{
int i=4;
int j=10;

i++;

if (j > 0)
{
/* i defined in 'main' can be seen */
printf("i is %d\n",i);
}

if (j > 0)
{
/* 'i' is defined and so local to this block */
int i=100;
printf("i is %d\n",i);
}/* 'i' (value 100) dies here */

printf("i is %d\n",i); /* 'i' (value 5) is now visable.*/
}

This will generate following output
i is 5
i is 100
i is 5

Here ++ is called incremental operator and it increase the value of any integer variable by 1. Thus i++ is equivalent to i = i + 1;

You will see -- operator also which is called decremental operator and it decrease the value of any integer variable by 1. Thus i-- is equivalent to i = i - 1;

Global Variables
Global variable is defined at the top of the program file and it can be visible and modified by any function that may reference it.

Global variables are initialized automatically by the system when you define them!

Data Type Initialser
int 0
char '\0'
float 0
pointer NULL

If same variable name is being used for global and local variable then local variable takes preference in its scope. But it is not a good practice to use global variables and local variables with the same name.

int i=4;                 /* Global definition */

main()
{
i++;                     /* Global variable */
func();
printf( "Value of i = %d -- main function\n", i );
}

func()
{
int i=10;               /* Local definition */
i++;                      /* Local variable */
printf( "Value of i = %d -- func() function\n", i );
}

This will produce following result
Value of i = 11 -- func() function
Value of i = 5 -- main function

i in main function is global and will be incremented to 5. i in func is internal and will be incremented to 11. When control returns to main the internal variable will die and and any reference to i will be to the global.

NEXT >> Storage Classes

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