Programming and Data Structures

346 Programming and Data Structures

pointer 'q' contains the base address of u [ ]. Hence, pointers p and q are global pointers. They can

be accessed through any function.

10.10 RECURSION

The C language supports recursive feature, that is, a function is called repeatedly by itself. Recursion

can be used directly or indirectly. The direct recursion function calls to itself till the condition is

true. In indirect recursion a function calls to another function, then the called function calls to the

calling function.

10.31 Write a program to call the mainO function recursively and perform a sum of 1 to 5

numbers.

# include <8tdio.&>

# include <procaa*«h>

in t x # s;

void m a in (in t);

void main(x)

s=s+x;

p rin tf ( m\n x ® %d s - % d~,x,e);

i f (x*®5)

e x i t (0 );

tnaitt(++x);

>

OUTPUT:

x = 1 s = 1

x = 2 s = 3

x = 3 s = 6

x = 4 s= 10

x = 5 s= 15

Explanation In the above program variables x and y are declared outside main () function.

Initially their values are zero. Followed by it the prototype of function main () is defined. The

variable x is passed through the main () function. The variable x is added to variable s till value of

x reaches 5. Every time function main () is called repeatedly, x is incremented. The result of the

program is displayed at the output. The value of x in main () is 1 because it is a command line

argument.

Functions 347

Table 10.7 Steps of a recursive function

Function call Value of x Value of s (sum)

main(l)

x = 1

s= l ( 0 + 1 ) = 1

main(2)

x = 2 s=3 ( 2 + 1 + 0 ) = 3

main(3) x = 3

s=6 (3 + 2 + l + 0 ) = 6

main(4)

x = 4 s=10 (.4 + 3 + 2 + 1 + 0 ) = 10

main(5)

x = 5

s=15 (5 + 4 + 3 + 2 + l + 0 ) = 15

The recursive function main () is called as in Table 10.7. The analysis of each step is given for

understanding.

1032 Write a program to calculate triangular number of an entered number with recursion

function method.

# include <stdio.h>

# include <conio.h>

void mainO

{

int n , t , t r i num(int) ;

c lr s c r () ;

printf ("\n Enter a Number

scanf ("%d",&n);

t=trijnum(n);

printf ("\n Triangular number of %d is %d'r,n,t);

tri_num( m)

I int f=0;

if (m ~ 0 )

retumif);

else

f=f+m+trijnum(m -l);

return (f);

I

OUTPUT;

Enter a Number: 5

Triangular number 5 is 15

Explanation In the above program a number is entered whose triangular number is to be

calculated. The number is passed to the function tri_num (). The value of variable n is copied to

348 Programming and Data Structures

variable m. In the tri_n u m () function the entered number is added to variable f. The entered

number is decremented and the tri_n u m () function is called repeatedly (recursively) till the

entered number becomes zero.

10.33 Write a program to display the given string using recursive call of a user-defined

function.

# include <stdio.h>

# include <conio.h>

# include <process.h>

char • t r [ ] * <rHave a Good Day*;

in t x*0;

void m ain(vo id);

void main ()

{

$2vitch(str[x])

{

case 'H':

clrscrO;

default:

printf ("%c",str[x]);

break;

case '\0':

exit(l);

break;

I

x++;

mainO;

OUTPUT;

Have a Good Day

Explanation In the above program a string "Have a Good Day" is initialized with character

array str[]. The integer variable x is initially zero. The mainO function is called recursively. In

each call variable x is incremented. The switch () case structure controls display of string. If the

first character is H, screen is cleared. The default case displays each character where x is the element

number. If the 0 character is encountered, the program terminates. In the first case break statement

is not taken to execute successive case statements, so that the screen is cleared and the complete

string is displayed