Answer to Question #100831 in C++ for zahra

Question

Write a program that will display the result of n! using a loop. For example,if the user enters 5 for
n, the program should display “factorial of is 120”. solve with while

Answer 1

/***************************************************************************************/

/** Example of a factorial function. */

/***************************************************************************************/

#include <iostream>

using namespace std;

int inputPosInt(string); //Input a positive integer with minimum verification.

unsigned long long factorial(int); //Function for calculating the factorial.

int main()

{

int d = inputPosInt("Please enter a positive integer: ");

unsigned long long l = factorial(d);

if(l == 0) //The function returns zero if the result is larger than ULLONG_MAX.

{

cout << "Too many to calculate factorial." << endl;

}

else

{

cout << "The factorial of " << d << " is " << l << endl;

}

return 0;

}

/******************************************/

/**Function for calculating the factorial.*/

/******************************************/

unsigned long long factorial(int d)

{

unsigned long long l = 1;

if(d == 0) return 1;

do

{

l*=d--;

if((d>0)&&((ULLONG_MAX/d)<l)) return 0; //Return zero if the result is larger than ULLONG_MAX

}while(d>0);

return l;

}

/** Function for entering a value of type "int" with validation. */

/** The string in the argument is needed to prompt for data entry. */

int inputPosInt(string s)

{

int d;

bool b;

do{

b = true;

cout << s;

cin >> d;

if(!cin) //If incorrect characters are entered, then clear the input buffer and ask to enter again.

{

cout << "The input is not correct. Try again.\n";

cin.clear();

while (cin.get() != '\n');

}

else

{

if(d >= 0)

{

b = false;

}

else

{

cout << "The input is not correct. Try again.\n" << endl;

cin.clear();

while (cin.get() != '\n');

}

}

}while(b);

return d;

}