C++ Program to find factorial of Number 

 Find factorial of  a Number in C++

Program to find factorial of Number in C++

What is a Factorial of a number ‘n’?

The factorial of a number ‘n’ is the product of all number from 1 upto the number ‘n’

it is denoted by n!. 

For example:

4! = 4*3*2*1 = 24  

6! = 6*5*4*3*2*1 = 720    

C++ programs:

Source code:

#include<iostream>

/*  iostream provides basic

input and output services for C++ programs */

using namespace std;

int main()

// Th execution of program start with the main function 

 {

    int num,factorial=1;

//Variable Declarations specify the type followed by the name

//Initialization is the process of assign the value to a variable

   cout<<" Enter Number To Find Its Factorial:  ";

// cout is used to display the same statement in the output.

    cin>>num;

// cin is used to enter the value by the user.

    if (num < 0)

/* The if/else statement executes a block

 of code if a specified condition is true. 

If the condition is false, another block 

of code can be executed*/

   cout << "Error! Factorial of a negative number doesn't exist.";

    else {

    for (int a=1;a<=num;a++)

    // for loop

     {

        factorial=factorial*a;

    }

    cout<<"Factorial of " <<num <<" is :"<<factorial<<endl;

    return 0;

}   

}

In this program, we take a positive integer from the user and compute the factorial using for loop. We print an error message if the user enters a negative number.
When the user enters a positive integer  for loop is executed and computes the factorial. The value of a is initially 1.
The program runs until the statement a <= num becomes false.