Scope of variables

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2. Disclaimer: This presentation is prepared by trainees of baabtra as a part of mentoring program. This is not official document of baabtra –Mentoring Partner Baabtra -Mentoring Partner is the mentoring division of baabte System Technologies Pvt . Ltd

3. Variable In  computer programming, a  variable  is a storage location The variable name is the usual way to reference the stored value Element of the Programing Language .

4. Variable( cntnd ) Hold data temporary . Value Lost as soon as program terminate Declaration : data type variable name ; int a;

5. S cope The scope of a variable is the block of code where the variable is valid for use If declaration is made outside the bodies of all functions and outside the main program is called global variable A local declaration is one that is made inside the body of a function It is possible to declare the same identifier name in different parts of the program

6. Scope( cntnd ) Undisciplined use of global variables may lead to confusion and debugging difficulties The use of global variable is not encouraged due to the lack of protection of data

7. Scope of Variables Scope refers to the visibility of variables. 3 places where variables can be declared in C programming language: Inside a function or a block - local  variables Outside of all functions -   global   variables In the definition of function parameters - formal  parameters.

8. Local variables Declared inside a function or Block. They are unknown to other functions and to the main program They are recreated each time a function is executed or called . They can be used only by statements that are inside that function or block of code.

9. Example int sum( int a , int b ) { int total ; total= a+b ; }

10. Global variable Declared out side of all Functions used within the program A global variable can be accessed by any function . They remains in the memory as long as the program is executing. They do not get recreated if the function is recalled . i.e. a global variable is available for use throughout your entire program after its declaration.

11. Global variable eg :- #include < stdio.h > void get_students ( void ) ; int num_stud ; main () { get_students () ; printf ( "The number of students is %d\n", num_stud ) ; } void get_students ( void ) { num_stud = 12 ; }

12. LOCAL VARIABLES Vs GLOBAL VARIABLES Using local variables allows to focus attention on smaller more manageable pieces of the program. Globals forces to keep track of how they're being used throughout the entire system. While working with other people, you must coordinate who's creating which global variables. It is not valid to create two globals of the same name. The effects of algorithm steps reduces the cases of unexpected behavior . Localizing the effects of algorithm steps makes the program easier for others to understand.

13. Difference between Global and Local Variables #include< stdio.h > int sum( int , int ); int total ; // Global variable declaration main(){ int a,b ; // Local variable declaration a=10,b=5; // initialization total =sum( a,b ); Printf (“% d”,total ); // Print result } sum( int c, int d){ total = c+d ; return total ; }

14. Example #include< stdio.h > int f1(); int a=10; main() { int a=20; int b=f1(); printf (“%d\n % d”, a , b); } f1( int x) { x=a; return x; } Using local variable ‘a’ Using global variable ‘a’ Output 20 10

15. A Final Implementation with an Example #include <stdio.h> int f1( void ) ; int f2( int x, int a ) ; int a ; main() { int a, b, c ; a = 7 ; b = f1() ; c = f2( a, b ) ; printf( "%d\n %d\n %d\n", a, b, c ) ; } int f1( void ) { a = 12 ; printf( "%d\n ", a ) ; return( a + 5 ) ; } int f2( int x, int a ) { printf( "%d\n ", a ) ; return( x * a ) ; } OUTPUT 12 17 7 17 119 a =12 a=7 b=17 x =7 a =17 c =119

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