A program to calculate factorial for big numbers
C++ Program to calculate Factorial for big numbers : One fine day I was trying to get factorial of some number ( >300) and couldn't find it on any tool . Most of the open tools had some limitations, so I decided to write my own program and thought of sharing it :) Of course this is a program written in less than half an hour or so, hence don't expect it to be most efficient OR wonderfully written wrt language constructs. It did what I wanted at that moment and fulfilled its purpose :)
------------ code starts here -------------
#include < iostream >
#ifndef ARRAY
#include < vector >
#endif
/* @author : Manish Baphna < manish.baphna@gmail.com >
* @brief : This program calculates factorial of given number. There are already available tools for that
* but most of them have some limitations like upper limit on number (e.g. google online calculator
* doesn't calculate factorial for numbers bigger than 170 : type 171! on google and search!! )
* This program is just an effort to give better results. Use this @your own risk :)
*
* @warning :I am sharing this program ONLY because I think its better to share it instead of just keeping in
* my drive. This code is written in haste and NOT WRITTEN to explain things. So if you are looking
* for too many comments and nice formatting, please excuse me. How ever , constrcutive suggestions
* are most welcome. BUGS are most most most welcome !
*/
//! This is the main sizing factor here. Using SIZE = 10K , I can find max fact of 3249 ( 10,000 digits ) .
//! If you have bigger number than 3249 then increase SIZE to few ZEROs :) How much, that you have to try and learn
//! If you get glibc error for a number , it means you need bigger SIZE.
#define SIZE 10000
using namespace std ;
/*!
* @brief This is the main function which does all calculation. This function has two implementation , default is
* vector based , other is ARRAY based. What essentially is done here is the alternate storage mechanism
* for results. For big factorials , int / long are insufficient so this method stores them in a BIG variable
* called 'array' which is actually sequence of integers . (Note: ARRAY is compile time switch)
* @param N the number for which you want to find factorial
*/
void myfact(int N){
#ifdef ARRAY
cout << " \n Array Form \n------------------------------\n" ;
int array[SIZE] ;
memset(array,0x0,SIZE) ;
array[0] = 1 ;
#else
cout << " \n Vector Form \n------------------------------\n" ;
vector array(SIZE,0) ;
array[0] = 1 ;
#endif
int count = 1 ;
int xcount = 1 ;
int temp = 0 , carry = 0 ;
int num = 2;
while(num <= N){
carry = 0 ;
count = xcount ;
for(int i=0; i< count; i++){
temp = array[i] * num + carry ;
if(temp>= 10) {
array[i] = temp % 10 ;
carry = temp / 10 ;
xcount = i+1+1 ;
}else{
array[i] = temp ;
carry = 0;
}
}
while(carry>0){
array[count++] = carry%10 ;
carry = carry/10 ;
if(carry) xcount++ ;
}
num++ ;
}
for(int j=0; j< xcount ; j++){
cout << array[xcount -1 - j ] ;
}
cout << "\n digits required " << xcount-1 << endl ;
}
int main(int argc, char *argv[]){
if(argc !=2 ){
cout << "pgm " << endl << " e.g. : pgm 200 " << endl ;
exit(1) ;
}
int num = (atoi)(argv[1]) ;
cout << " returning factorial of " << num << endl ;
myfact(num) ;
return 1;
}
------------ code starts here -------------
#include < iostream >
#ifndef ARRAY
#include < vector >
#endif
/* @author : Manish Baphna < manish.baphna@gmail.com >
* @brief : This program calculates factorial of given number. There are already available tools for that
* but most of them have some limitations like upper limit on number (e.g. google online calculator
* doesn't calculate factorial for numbers bigger than 170 : type 171! on google and search!! )
* This program is just an effort to give better results. Use this @your own risk :)
*
* @warning :I am sharing this program ONLY because I think its better to share it instead of just keeping in
* my drive. This code is written in haste and NOT WRITTEN to explain things. So if you are looking
* for too many comments and nice formatting, please excuse me. How ever , constrcutive suggestions
* are most welcome. BUGS are most most most welcome !
*/
//! This is the main sizing factor here. Using SIZE = 10K , I can find max fact of 3249 ( 10,000 digits ) .
//! If you have bigger number than 3249 then increase SIZE to few ZEROs :) How much, that you have to try and learn
//! If you get glibc error for a number , it means you need bigger SIZE.
#define SIZE 10000
using namespace std ;
/*!
* @brief This is the main function which does all calculation. This function has two implementation , default is
* vector based , other is ARRAY based. What essentially is done here is the alternate storage mechanism
* for results. For big factorials , int / long are insufficient so this method stores them in a BIG variable
* called 'array' which is actually sequence of integers . (Note: ARRAY is compile time switch)
* @param N the number for which you want to find factorial
*/
void myfact(int N){
#ifdef ARRAY
cout << " \n Array Form \n------------------------------\n" ;
int array[SIZE] ;
memset(array,0x0,SIZE) ;
array[0] = 1 ;
#else
cout << " \n Vector Form \n------------------------------\n" ;
vector
array[0] = 1 ;
#endif
int count = 1 ;
int xcount = 1 ;
int temp = 0 , carry = 0 ;
int num = 2;
while(num <= N){
carry = 0 ;
count = xcount ;
for(int i=0; i< count; i++){
temp = array[i] * num + carry ;
if(temp>= 10) {
array[i] = temp % 10 ;
carry = temp / 10 ;
xcount = i+1+1 ;
}else{
array[i] = temp ;
carry = 0;
}
}
while(carry>0){
array[count++] = carry%10 ;
carry = carry/10 ;
if(carry) xcount++ ;
}
num++ ;
}
for(int j=0; j< xcount ; j++){
cout << array[xcount -1 - j ] ;
}
cout << "\n digits required " << xcount-1 << endl ;
}
int main(int argc, char *argv[]){
if(argc !=2 ){
cout << "pgm
exit(1) ;
}
int num = (atoi)(argv[1]) ;
cout << " returning factorial of " << num << endl ;
myfact(num) ;
return 1;
}
posted by Manish Baphna at 10:44 PM
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