Chapter 2.4 - Discuss how variables are used in a program | Part -1

DECLARATION OF VARIABLES

After designing suitable variables names, we must declare them to the compiler.

The declaration does two things:

1. It tells the compiler what the variable name is.
2. It specifies what type of data the variable will hold.

The declare of variables must be done before they are used in the program.

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Primary Type Declaration

A variable can be used to store a value of any data type. That is, the name has nothing to do with its type. The syntax  of declaring a variable is as follows:

data-type v1,v2,....vn

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v1,v2,...vn are the names of variables. Variables are separated by commas. A declaration statement must end with a semicolon. For example, valid declarations are:

int count;            

int number, total;

double ratio;       

int and double are the keywords to represent integer type and real type data values respectively. Table 2.9 shows various data types and their keywords equivalents. #variables_in_c

  

The program segment given in Fig 2.7 illustrates the declaration of variables. main() is the beginning of the program. The opening brace { single the execution of the program. Declaration of variables is usually done immediately after the opening brace of the program. The variables can also be declared outside (either before or after) the main function. The importance of the place of the declaration will be dealt with in detail later while discussing functions. #allaboutprogramming62

Note-: C99 permits declaration of variables at any point within  a function or block, prior to their use

When an adjective (qualifier) short, long, or unsigned is used without a basic data type specifier, C compilers treat the data types as an int. If we want to declare a character variable as unsigned, then we must do so using both the terms like unsigned char

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Default values of Constants 

Integer constants, by default, represent int type data. We can override this default by specifying unsigned or long after the number (by appending U or L) as shown below:

Literal                             Type                                      Value

+111                                int                                           111

-222                                 int                                           -222

45678U                           unsigned int                           45678

-56789L                           long int                                  -56789

987654UL                       unsigned long int                   987654

Similarly, floating point constants, by default represent double type data. If we want the resulting data type to be float or long double, we must append the letter f or F to the number for float and letter l or L long for long double as shown below:

Literal                             Type                                      Value

0.                                     double                                     0.0

-222                                 double                                     0.0

45678U                           double                                     12.0

-56789L                          double                                     1.234

987654UL                       float                                       -1.2

1.23456789L                   long double                          1.23456789


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