Variables

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A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in C has a specific type, which determines the size and layout of the variable's memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable.

There are various other types of data types that we will cover in subsequent chapters.

Rules for Constructing Variable Names

• It is any combination of 1 to 31 alphabets, digits or underscores.

• It must start with an alphabet or underscore

• No commas or blanks are allowed within a variable name

• No special symbols other than an underscore is allowed

E.g. average_salary first_name lastName

Variable Declaration

All variables must be declared before we use them in C program, although certain declarations can be made implicitly by content. A declaration specifies a type, and contains a list of one or more variables of that type as follows: type variable_list; type is a valid C data type including char, int, float, double, or any user defined data type etc., and variable_list may consist of one or more identifier names separated by commas.

E.g. int name,subjects,div; char ch; float average,percentile; double result;

Initialization at the time of declaration. int subjects = 4; Though you can declare a variable multiple times in C program but it can be decalred only once in a file, a function or a block of code.

Variable Initialization

Variables are initialized (assigned an value) with an equal sign followed by a constant expression. The general form of initialization is:

variable_name = value;

Variables can be initialized (assigned an initial value) in their declaration. The initializer consists of an equal sign followed by a constant expression as follows:

type variable_name = value;

E.g.  int d = 3, f = 5; /* initializing d and f. */

       byte z = 22; /* initializes z. */

       double pi = 3.14159; /* declares an approximation of pi. */

       char x = 'x'; /* the variable x has the value 'x'. */

It is a good programming practice to initialize variables properly otherwise, sometime program would produce unexpected/random result.

E.g.

#include <stdio.h>
void main ()
{
  /* variable declaration: */
  char a;
  int b,c;
  int sum;
  float d;
 
  /* actual initialization */
  a = ‘a’;
  b = 10;
  c = 20;
  sum = a + b;
  printf("Value of sum : %d \n", sum);
  f = 70.0/3.0;
  printf("Value of f : %f \n", f);
 
  printf(“Value of character a is %c”,a);
  getch(); // use return 0 for int main()
}