C Tutorial

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Scope of variables in C

Introduction

The scope of variables in C can be defined as the scope of reach of a variable, the term scope is used to determine the visible range of an object. By region or visible range in a program we meant that it is a space where a variable is declared and used.

Based on this, there are a total of three types of scopes in which variables can be classified. They are as follows:

  1. Local variables
  2. Global variables
  3. Formal parameters

The types are dependent on the region where the declaration of variable is made and used

  • Local variables : are defined inside a function or a block
  • Global variables :  are outside all functions.
  • Formal variables : are defined in function parameters

The term scope is used to determine the visible range of an object. It is basically a definition of visibility. In simple terms, it is used to define the range where an object can be accessed.

In C programming, the scope of variable is either local or global

  • A scope is said to be local if the definition of variable is within the block. The variable is visible only within the block it is defined. The visibility lies within the block.
  • A scope is said to be global if the variable is visible from their definition until the end of the program. The visibility of global variables is from definition to end of program. It is visible everywhere in the program.

 

Example

#include<stdio.h>
int c = 5; // global area (can be accessed anywhere throughout the program)
int main () {
   int a = 10; // local scope
   printf ("a=%d", a);
   printf ("c=%d", c);
   function ();
}
function (){
   printf ("c=%d",c); // global variable
}

Local Variables

Variables that are declared inside a function or block are called local variables. The range of local variables lies within the block, i.e., local variables are only accessible to statements that are inside that function or block of code.

The functions outside of local variables are unbound to them.

Program 1:

#include <stdio.h> // header files
 
int main () {


  int a, b;  // declaration of local variables
  int c;
 
  a = 10;   // actual initialization 
  b = 20;
  c = a + b;
 
  printf ("value of a = %d, b = %d and c = %d\n", a, b, c);
 
  return 0;
}

The following example shows how local variables are used. Here all the variables a, b, and c are local to main() function.

Global Variables

Global variables are defined outside a function or any specific block, in most of the case, on the top of the C program. The scope of global variables is global and they hold their values all through the end of the program. The accessibility of global variables is within any of the functions that are declared or defined within the program by the programmer.

The term global access means that any function can access variables defined within the global scope, i.e., the visibility is for the entire program.

Program 2 :

#include <stdio.h> // header files declaration


int z;  // declaration of global variable
 
int main ()
{
     int x,y; // local variable definition and initialization
      
    x = 20;   
    y = 30;
    z = x + y;
     
    printf ("value of x = %d, y = %d and z = %d\n", x, y, z);
     
    return 0;
}

Note: The visibility of global variables is for the entire program

Global Variable Initialization

First the definition of local variable takes place and after the definition, there is no initialization of any value to the variable by either the system or the compiler. This has to be performed manually, i.e., initialization of variables has to be done by the programmer. But talking about the global variables, they are not manually initialized like the former. They are automatically defined by the.

The following table is a representation of how global variables are defined. It is based on their data types.

datatypeInitial Default Value
int0
char'\0'
float0
double0
pointerNULL

A variable name consists of an individual character set or combination of character sets. In simple terms, the name of a variable can be composed of letters, digits, and a special character (underscore character).

Note: The variable name must begin with either a letter or an underscore.

The basic variable types in C are as follows

Sr.No.Variable Type Description
1int (Integer)   Stands for integer and it is a data type which is used for variable declarations or declaration of functions of different types
2float  Float is a data type which is used to represent floating point quantities or numbers .  
3char  Typically a single octet(one byte). It is an integer type
4doubleA double-precision floating point value.
5void  Represents the absence of type.  

In the C programming language, there exists a path which allows us (the programmer) to define various other types of variables. These types are Pointer, Array, Enumeration, Structure, Union, etc.

Program 2: Sum and product of of two floating numbers

#include<stdio.h>
#include<conio.h>


void main( )
{
  
  float num1, num2, sum, product;  //floating variables declaration
  
  printf("Enter the first number: "); // printing the first float type number
  scanf("%f",&num1);       
  
  printf("Enter the second number: "); // printing the second float type number
  scanf("%f",&num2);


   sum = num1+num2;    //calculating the sum of two numbers
   product = num1*num2;  //calculating the sum of two numbers


  printf("The Sum of two numbers = %f",sum); // printing the sum of float type numbers
  printf("\n The Product of two numbers = %f",product); // printing the product
  getch( );

Example of variable types in C:

Char in C

Example:

Suppose there is an array of size 10 and we need to store a string “computer” inside it. This can be simply done using the following piece of code;

char a[10] = "computer";

When this piece of code is executed, an array of size 10 is created with string “computer” inside it which looks something like this;

computer\0 

Here, the ‘\0’ is used to indicate the end of a string.



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