C++ Language program to calculate factorial of a number using for loop

Introduction: In previous articles i explained What is For loop in C++ Language? Example program to print counting up to given limit and Print table of entered number using For loop and What is goto statement in C++ Language,its advantages and disadvantages with program example and Find greatest of three numbers using multiple if and Else if ladder to perform operation on two numbers based on operator and Find week day corresponding to number using switch case.

In this article i will explain How to write/create a program to find/get/calculate factorial of entered number using For loop in C++ language.

Description:  To calculate factorial of number, simply multiply  from 1 to that number or that number to 1 i.e. the factorial of a number 'n' is the product of all number from 1 up to the number 'n' or from 'n' up to 1 and it is denoted by n!.

Rule: n! = n*(n-1)!

So 1! = 1

     2! = 2×1 = 2

     3! = 3×2×1 = 6

     4! = 4×3×2×1 = 24

     5! = 5×4×3×2×1 = 120

  For example if n=6 then factorial of 6 will be calculated as 1*2*3*4*5*6= 720 or 6*5*4*3*2*1=720.  So 6 != 720.

Implementation: Let's create a C++ program to calculate Factorial of a number.

#include<conio.h>

#include<iostream.h>

int main()

{

    clrscr();

  unsigned long long int  fact=1;

  int i,n;

  cout<<"Enter any positive number to calculate its factorial: ";

  cin>>n;

  for(i=n;i>=1;i--)

  {

    fact=fact*i;

  }

  cout<<"\nFactorial of " <<n<<" = "<<fact;

  getch();

  return 0;

} 

Note:  We can also use 

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

  {

    fact=fact*i;

  }  

instead of 

for(i=n;i>=1;i--)

  {

    fact=fact*i;

  }  
in the above program to calculate the factorial of a number.

• Run the program using Ctrl+F9

 Output:

 Enter any positive number to calculate its factorial: 5

  Factorial of 5 = 120

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