Programming languages - C Programming

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Lesson Description

Lession - #7 C Variables

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.
The name of a variable can be formed of letters, digits, and the underscore character. It must begin with either a letter or an underscore. Upper and lowercase letters are distinct because C is case-sensitive. Based on the basic types explained in the previous chapter, there will be the following basic variable types −
Sr.No. Type & Description
1 char Typically a single octet(one byte>
. It is an integer type.
2 int The most natural size of integer for the machine.
3 float A single-precision floating point value.
4 double A double-precision floating point value.
5 void Represents the absence of type.

Variable Definition in C
A variable definition tells the compiler where and how much storage to create for the variable. A variable definition specifies a data type and contains a list of one or more variables of that type as follows −

type variable_list;
Here, type must be a valid C data type including char, int, float, double, bool, or any user-defined object; and variable_list may consist of one or more identifier names separated by commas. Some valid declarations are shown here −

int    i, j, k;
char   c, ch;
float  f, salary;
double d;
The line int i, j, k; declares and defines the variables i, j, and k; which instruct the compiler to create variables named i, j and k of type int.
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;
Some examples are −

extern int a = 3, b = 5;    // declaration of a and b. 
int a = 3, b = 5;           // definition and initializing a and b. 
byte s = 22;                // definition and initializes s. 
char t = 'x';               // the variable t has the value 'x'.
Variable Declaration in C

A variable declaration provides assurance to the compiler that there exists a variable with the given type and name so that the compiler can proceed for further compilation without requiring the complete detail about the variable. A variable definition has its meaning at the time of compilation only, the compiler needs actual variable definition at the time of linking the program.


The following example, where variables have been declared at the top, but they have been defined and initialized inside the main function −

#include <stdio.h>

// Variable declaration:
extern int a, b;
extern int c;
extern float f;

int main (>
{ /* variable definition: */ int a, b; int c; float f; /* actual initialization */ a = 10; b = 20; c = a + b; printf("value of c : %d \n", c>
; f = 70.0/3.0; printf("value of f : %f \n", f>
; return 0; }
When the above code is compiled and executed, it produces the following result −

value of c : 30
value of f : 23.333334
The same concept applies on function declaration where you provide a function name at the time of its declaration and its actual definition can be given anywhere else. For example −

// function declaration
int func(>
; int main(>
{ // function call int i = func(>
; } // function definition int func(>
{ return 0; }