C Language

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C - Language Theory

Variables

Variables are name of the memory location. It is used to store data.

Basic Data Types:-

Size and Range of Data Types

Data typesSize in BytesRangeFormat
Signed Char1-128 to 127%c
Unsigned Char10 to 255%c
Short Signed Int2-32768 to -32767%d
Short Unsigned Int20 to 65535%u
Signed Int2-32768 to -32767%d
Unsigned Int20 to 65535%u
Long Signed Int4-2147483648 to +2147483647%Ld
Long Unsigned Int40 to 4294967295%Lu
Float43.4e-38 to 3.4e+38%f
Double81.7e-308 to 1.7e+308%Lf
Long Double103.4e-4932 to 1.1e+4932%LF

Rules for defining variable

  1. Variable type can be char, int, float, double.
  2. A variable name can consist of alphabets, digits and the underscore character.
  3. Variable name can start with alphabet, and underscore. It can not start with a digit.
  4. Blank spaces cannot be used in variable names.
  5. Special characters like $, # are not allowed.
  6. Keywords are not allowed as variable name, i.e int, float, char, etc.

Local Variable

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

Syntax
Void function1()
{
int x=5;//local variable
}

Global Variable

A variable that is declared outside the function or block is called a global variable.

Syntax
{ int a=10;//global variable
}

Static Variable

A variable that is declared with the static keyword is called static variable. It retains its value between multiple function calls.

Syntax
void function1()
{ int x=5;//local variable
static int y=5;//static variable
x=x+1
y=y+1
printf ("%d,%d",x,y);

}

Note: if you call the function many times, the local variable prints the same value in each function ie 6, 6, 6 and so on. But in static variable prints the increment value in each function i.e 6, 7, 8 and so on.

Automatic Variable

All variables in C that are declared inside the block. are automatic variables by default. We can explicitly declare an automatic variable using auto keyword.

Syntax
void function1()
{ int x=5;//local variable (also automatic)
auto int y=6;// automatic variable
 }

External Variable

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

Syntax
#include<stdio.h>
void print()
{ extern int g = 10;
 printf ("g=%d\n",g);

}
int main()
{ g = 7;
printf ("g=%d\n",g);
printf ();
return 0;
 }