51.Recursion, Visibility and scope of variables,Local variables

 

Recursion:

Executing a statement or multiple statements repeatedly is called iteration or loop.

A loop can be build either by using any iterative control structure or recursion.

Recursion is executing a statement or multiple statements repeatedly by calling a function on itself.

To solve simple problems iterative control structure is better comparatively with recursion.

Some times complex problems may be easily solved using recursion.

Example1:

 

 

 

 

 

 

 

 

Output:

Hello world…………….

 

Note: Use ctrl+break to stop the program.

 

Example2:

 

 

 

 

 

 

 

 

 

 

Output:

1          2          3………..

 

Note: Use ctrl+break to stop the program.

 

Example3:

#include<stdio.h>

int x=1;

void main()

{

   printf("\t%d",x);

   x++;

   if(x<=5)

       main();

   getch();

}

 

Output:

1          2          3          4          5

Specification1:

Print the sum of natural numbers using recursion.

Program:

#include<stdio.h>

int sum(int);

void main()

{

  int n,sm;

  clrscr();

  printf("Enter the limit:");

  scanf("%d",&n);

  sm=sum(n);

  printf("Sum %d",sm);

  getch();

}

int sum(int n)

{

   int s;

   if(n==1)

        return 1;

   s=n+sum(n-1);

   return s;

}

 

Execution:

Enter the limit: 5

Sum 15

 

 

Example explained:

Here the sum function calls on itself.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Specification2:

Accept an integer and print its factorial using recursion.

 

Program:

#include<stdio.h>

long int factorial(int);

void main()

{

   int n;

   long int fact;

   clrscr();

   printf("Enter any integer:");

   scanf("%d",&n);

   fact=factorial(n);

   printf("Factorial %ld",fact);

   getch();

}

long int factorial(int n)

{

    long int f;  

       if(n==1)

          return 1;

   f=n*factorial(n-1);

   return f;

}

 

Execution:

Enter any integer: 8

40320

 

Visibility and scope of variables:

Visibility is how far a variable is accessible.

Scope is the life of variable that is when is allocated and de-allocated.

According to the visibility and scope variables are classified into

1. Local variables
2. Global variables
3. Block variables.

 

Local variables:

Variables declared with in a function are called local variables.

The visibility of local variables is limited to the function.

Local variables belongs to one function can't be accessed into another function.

Scope (life) of local variables is limited to the function.

Memory allocation of local variables allocates at the beginning of function execution and de-allocates at the end of function execution.

 

Example1:

/* visibility of local variable */

#include<stdio.h>

void main()

{

int x=10;

clrscr();

display();

getch();

}

void display()

{

 printf("x=%d",x); 

}

 

Output:

Error: undefined symbol "x" in function display()

 

Example explained:

"x" is the local variable to main(), can't be accessed into display() because the visibility of "x" is limited to the main() function.

 

Example2:

/* visibility of local variable */

#include<stdio.h>

void main()

{

 int x=40;

 clrscr();

 printf("x=%d",x);

 process();

 printf("\nx=%d",x);

 getch();

}

void process()

{

 int x=80;

 printf("\nx=%d",x);

}

 

Output:

x=40

x=80

x=40

 

 

Example explained:

"x" is declared for two times that is in main() and process().

They are different; visibility of which is limited to their home functions.

 

Example3:

/* scope of local variables */

void display(int);

void main()

{

int i;

clrscr();

for(i=1;i<=5;i++)

    display(i);

getch();

}

void display(int x)

{

int a=100;

a=a+x;

printf("\t%d",a);

}

 

Output:

101      102      103      104      105

 

Example explained:

Because "a" is a local variable to display(), memory allocation of which is allocated at the beginning of function execution and de-allocates on completion of function execution.

The value of "a" is not preserved for next iterations.