C++ Tutorials - Absolute n00b spoonfeed

We just finished doing some probability stuff in school and i thought id write some code to do some of the work. They are all in long doubles because i wanted it to be able to do probabilities for like 52 cards. I dunno if these functions alrdy exist but here is my attempt. nCr is combinations, nPr is permutations.

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long double nCr(int n, int r) {

long double r_value;
long double num   = 1;
long double den_1 = 1;
long double den_2 = 1;
int n_r = n - r;

   while (n > 1) {

   num = num * n;

   n--;

   }

   while (r > 1) {

   den_1 = den_1 * r;

   r--;

   }

   while (n_r > 1) {

   den_2 = den_2 * n_r;

   n_r--;

   }

   r_value = num/(den_1 * den_2);

return r_value;

}


long double nPr(int n, int r) {

long double r_value;
long double num = 1;
long double den = 1;
int n_r = n - r;

   while (n > 1) {

   num = num * n;

   n--;

   }

   while (n_r > 1) {
   
   den = den * n_r;
   
   n_r--;

   }

   r_value = num/den;

return r_value;

}