Program Factorial by Loop and Recursion Versions

 Program FACTORIAL by RECURSION METHOD

Recursive Function Factorial of number in C++ programming recursion version

What is Recursion

When a function in C++ calls itself, it is called Recursive Function and the process of calling a function itself is called Recursion.
A method of defining a function in terms of its own definition is called recursion.

Advantages of using Recursion in C++

1. Recursion is a good problem solving technique in programming
2. It is based on the concept to solve a problem by reducing the problem to smaller sub-problems;
3. This results in recursive calls. In each successive recursive call the problem is reduced to more smaller sub-problem.
4. Recursive algorithms are simple to understand
5. Recursive algorithms are easy to implement

• Example: the Fcatorial of a non negatve number

  Base case in Recursion

   Recursion needs a base-case in order to stop

Recursive case

Recursion needs a recursive case to call a function itself to reduce problem into sub-problems

• fact(n) = n x fact(n-1)       Recursive part / recursive case of recursion
• fact(0) =  1                Terminating condition part also called base case
• In programming recursion is a method call to the same method. In other words, a recursive method     is one that calls itself.
• Why write a method that calls itself?

• But! Recursive calls can result in a an infinite loop of calls
• recursion needs a base-case in order to stop    , example fact(0) = 1, if n=0 then factorial =1
as we know that factorial of 0 is 1.
A recursive function to find factorial of a number works by calling itself
Example: if n>0 the factorial(n) = n x factorial (n-1)
as we know n! = n x (n-1)!

 /*
Write a C++ Program to input a positive number,
Calculate and display factorial of this number
by recursion.

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*/
#include<iostream.h>

#include<conio.h>

long  factorial(int n);
void main()
{

  clrscr();

  int number, counter;
 

  label1:
 
  cout<<"\n Enter the Number = ";

  cin>>number;

  if ( number < 0)
  {
  cout<<"\n Enter a non negative number, please!";
  goto label1;
  }
  cout<<"\n\n ----------- Results ------------";

  cout<<"\n\n The Factorial of the number "<<number<<"\n is "<<factorial(number);

  getch();

}

long factorial(int n)

{

    if ( n == 0 )
        return 1;
    else
        return n * factorial(n-1);
}  

Factorial of a number in C++ for loop version for understanding Recursion Logic

/*
Write a C++ Program to input a positive number
Calculate and Display Factorial of this number
by For Loop.


For Free C++ Programming Techniques (Example Programs), visit
Www.EasyCppProgramming.Blogspot.Com

and For Good Notes
Visit   Www.ForFreeEducation.Blogspot.Com
*/
#include<iostream.h>

#include<conio.h>

void main()
{

  clrscr();

  int number, counter;
  long int factorial;

  cout<<"\n Enter the Number = ";

  cin>>number;

  factorial = 1;
  for (counter = 1; counter <= number; counter++)
           factorial = factorial * counter;

  cout<<"\n\n ----------- Results ------------";

  cout<<"\n\n The Factorial of the number "<<number<<"\n is "<<factorial;

  getch();

}

You can download and install Turbo C++ 3.0 Compiler here
You can read the use of Writing, compiling, executing programs in C++ in Turbo C++ here

Download and Install Turbo C++ Full Screen Windows 7 Vista

You can find calculate factorial of a number program with while loop here
You can find calculate factorial of a number program with do while loop here

You can find calculate factorial of a number program using Recursion ( Recursive Factorial Function )