The document discusses recursion in C programming. It provides examples of internal and external recursion. Internally recursive functions call themselves, while externally recursive functions call other recursive functions. Examples are given to demonstrate recursion using static variables to avoid stack overflow issues. Methods for calculating power of a number and factorial using recursion are also presented. The document concludes with brief definitions of dangling pointers and function pointers.

1. Technical Chat
C Workshop
Day- 6

2. extern int g=5;
void abc()
{
int a;
static int s=5;
a=s--;
++g;
printf(“n %d %d %d”, a,s,g);
if(a>=3)
abc();
printf(“n %d %d %d”, a,s,g);
}
void xyz()
{
auto int a;
static int s;
a=++s;
--g;
printf(“n %d %d %d”, a,s,g);
if(a<=3)
xyz();
printf(“n %d %d %d”, a,s,g);
}
void main()
{
void xyz(void);
xyz();
abc();
}

3. O/p-
1 1 4
2 2 3
3 3 2
4 4 1
4 4 1
3 4 1
2 4 1
1 4 1
5 4 2
4 3 3
3 2 4
2 1 5
2 1 5
3 1 5
4 1 5
5 1 5

4. Classification of Recursion
● Internal Recursion Process
● External Recursion Process
● Whenever a recursion function is calling itself
then it is called internal recursion process.
● When one recursion function is calling another
recursion function then it is called external
recursion process.

5. extern int g=5;
void abc()
{
auto int a;
static int s=5;
a=s--;
++g;
printf(“n %d %d %d”, a,s,g);
if(a>=3)
abc();
printf(“%d %d %d”, a,s,g);
}
void main()
{
void xyz(void);
xyz();
}
void xyz()
{
int a;
static int s;
a=s++;
--g;
printf(“n %d %d %d”, a,s,g);
if(a<=1)
{
abc();
xyz();
}
printf(“n %d %d %d”, a,s,g);
}

6. O/p-
0 1 4
5 4 5
4 3 6
3 2 7
2 1 8
2 1 8
3 1 8
4 1 8
5 1 8
1 2 7
1 0 8
1 0 8
2 3 7
2 3 7
1 3 7
0 3 7

7. recursion by using main()
● By using auto variable it became stack overflow
● Because for every call auto variable will be
constructed.
void main()
{
int a= 5;
++a;
printf(“%d”, a);
if (a<=6)
main();
printf(“%d”,a);
}
O/p-
6666666666.........Stack overflow

8. void main()
{
static int s=2;
++s;
printf(“%d”,s);
if(s<=4)
main()
printf(“%d”,s);
}
O/p- 235555

9. Power of a number through recursion:
int power(int b, int e)
{
if (e<0)
return 0;
else if(e==0)
return 1;
else
return(b*power(b-e-1));
}
void main()
{
int a,b,p;
printf(“Enter value of a:”);
scanf(“%d”, &a);
printf(“Enter value of b:”);
scnaf(“%d”, &b);
p=power(a,b);
printf(“n %d^%d value is :
%d”, a,b,p);
}

10. Factorial through recursion.
void main()
{
int n,f;
int fact(int);
printf(“Enter a value:”);
scanf(“%d”, &n);
f=fact(n);
printf(“n %d fact value is: %d”,n,f);
}
int fact(int n)
{
if(n<0)
return 0;
else if(n<=1)
return 1;
else
return (n*fact(n-1));
}

11. Dangling Pointer
● A pointer variable which is pointing to a
dead or inactive location, is called
dangling pointer.

12. Function pointer
● A pointer variable which holds the address of the
function, is called function pointer.
● Function pointer calls are faster then normal
function calls.
● By using function pointer it is possible to pass a
function as a argument to another function.