Question

In C++, write a program that uses array to calculate the factorial of a reasonable large number (say, up to 2,000).

Answer 1

Screenshot

Program

//Header files for IO
#include <iostream>
using namespace std;
//Array holding Maximum digits
#define MAX_SIZE 50000
//Function prototypes
void findFactorial(int*,int&,const int);
void displayFactorial(const int[],const int ,const int);
//Main function
int main()
{
   //Declare array for result
   int factorialArray[MAX_SIZE];
   //Variable to keep track of size of the array
   int elementCnt;
   //Call function to find factorial
   findFactorial(factorialArray,elementCnt,1000);
   //call function to Display factorial
   displayFactorial(factorialArray, elementCnt, 1000);
}
//Function to find factorial of given number
void findFactorial(int* factorialArray, int& element,const int num){
   //Set result=0
   factorialArray[0] = 1;
   //Variable for each element
   element = 1;
   //Factorial finding loop
   for (int i = 2; i <= num; i++) {
       //Multiplication using school's method
       int carry = 0;
       for (int j = 0; j < element; j++)
       {
           int product = factorialArray[j] * i + carry;
           factorialArray[j] = product % 10;
           carry = product / 10;
       }
       while (carry)
       {
           factorialArray[element] = carry % 10;
           carry = carry / 10;
           element++;
       }
   }
}
//Function to display factorial
void displayFactorial(const int factorialArray[],const int elementsCnt,const int num) {
   cout << "Factorial of the number " << num << " is \n";
   for (int i = elementsCnt - 1; i >= 0; i--) {
       cout << factorialArray[i];
   }
   cout << endl;
}

------------------------------------------------------------------------

output

Factorial of the number 1000 is
402387260077093773543702433923003985719374864210714632543799910429938512398629020592044208486969404800479988610197196058631666872994808558901323829669944590997424504087073759918823627727188732519779505950995276120874975462497043601418278094646496291056393887437886487337119181045825783647849977012476632889835955735432513185323958463075557409114262417474349347553428646576611667797396668820291207379143853719588249808126867838374559731746136085379534524221586593201928090878297308431392844403281231558611036976801357304216168747609675871348312025478589320767169132448426236131412508780208000261683151027341827977704784635868170164365024153691398281264810213092761244896359928705114964975419909342221566832572080821333186116811553615836546984046708975602900950537616475847728421889679646244945160765353408198901385442487984959953319101723355556602139450399736280750137837615307127761926849034352625200015888535147331611702103968175921510907788019393178114194545257223865541461062892187960223838971476088506276862967146674697562911234082439208160153780889893964518263243671616762179168909779911903754031274622289988005195444414282012187361745992642956581746628302955570299024324153181617210465832036786906117260158783520751516284225540265170483304226143974286933061690897968482590125458327168226458066526769958652682272807075781391858178889652208164348344825993266043367660176999612831860788386150279465955131156552036093988180612138558600301435694527224206344631797460594682573103790084024432438465657245014402821885252470935190620929023136493273497565513958720559654228749774011413346962715422845862377387538230483865688976461927383814900140767310446640259899490222221765904339901886018566526485061799702356193897017860040811889729918311021171229845901641921068884387121855646124960798722908519296819372388642614839657382291123125024186649353143970137428531926649875337218940694281434118520158014123344828015051399694290153483077644569099073152433278288269864602789864321139083506217095002597389863554277196742822248757586765752344220207573630569498825087968928162753848863396909959826280956121450994871701244516461260379029309120889086942028510640182154399457156805941872748998094254742173582401063677404595741785160829230135358081840096996372524230560855903700624271243416909004153690105933983835777939410970027753472000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000