CODEWITHSUNDEEP
c++
MarshallLee
MarshallLee

Reputation: 1330

C++: How to properly print out the long long int using cout

I wrote a code to get the factorial of a number in C++.

Here is the code.

 #include <iostream>

 using namespace std;

 unsigned long long getFactorial(int);

 int main(int argc, char **argv) {
         int num = 5;
         unsigned long long factorial = getFactorial(a);

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

         return 0;
 }

 unsigned long long getFactorial(int num) {
         int i;
         unsigned long long factorial = 1;
         for(i=1; i<=num; i++) {
                 factorial *= i;
         }

         return factorial;
 }

When I assign 5 to the num value, it properly prints out the right value, 120. But when I assign bigger numbers, for example 100, it simply prints out 0. How can I modify the code to properly print out the result on the console?

Upvotes: 0

Views: 10408

Answers (1)

MarshallLee
MarshallLee

Reputation: 1330

Now I found the answer by myself.

By using the gmp library, it became much easier to deal with the big integers.

Here's the modified code.

#include <iostream>
#include <gmpxx.h>

using namespace std;

mpz_class getFactorial(int);

int main(int argc, char **argv) {
        int num = 100;
        mpz_class factorial = getFactorial(num);

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

        return 0;
}

mpz_class getFactorial(int num) {
        int i;
        mpz_class factorial = 1;
        for(i=1; i<=num; i++) {
                factorial *= i;
        }

        return factorial;
}

In order to use the gmp library, I included the <gmpxx.h> header file. Next I changed the data type of the factorial variable and the return type of the getFactorial() function from unsigned long long to mpz_class which is the data type that represents the big integer.

After modifying the code, I compiled with GCC using the following flags.

$gcc test.cpp -lstdc++ -lgmpxx -lgmp -o test

The -lgmpxx and -lgmp flags are required to compile the code using the gmp library.

Now it works fine.

Upvotes: 2

Related Questions