Problem of the Day
A new programming or logic puzzle every Mon-Fri

Today's objective is to create a function that takes in a number and uses a recursive algorithm to find the factorial of that number. Given the number 9 your program should output 362880.

Comments:

• Heroka - 10 years, 3 months ago

  In R:

  factorial <- function(n){
    if(n<=1){ #0! is also 1
      return(1)
    } else{
      return(n*factorial(n-1))
    }
  }
  
  > factorial(9)
  [1] 362880
  

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• David - 10 years, 3 months ago

  In C by switch.
  I like having 2 also be a base case, because something about bothering to multiply by 1 bugs me.
  Never the less:

  #include <stdio.h>
  
  unsigned int factorial(unsigned int);
  
  unsigned int factorial(unsigned int n) {
      int retval = 1;
      switch(n) {
          case 0:
              break;
          case 1:
              break;
          case 2:
              retval = 2;
              break;
          default:
              retval = n * factorial(n-1);
              break;
      }
      return retval;
  }
  
  int main(void) {
      printf("%i\n", factorial(9));
      return 0;
  }
  

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• Anonymous - 10 years, 3 months ago

  One of the most satisfying haskell example :D

  fac :: Int -> Int
  fac 1 = 1
  fac n = n * fac (n-1)
  

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• malboy - 10 years, 3 months ago

  Did this one in C#:

          int numUserInput,
              numAnswer;
  
          Console.WriteLine("Today's objective is to create a function that takes \n" +
              "in a number and uses a recursive algorithm to find the factorial \n" +
              "of that number. Given the number 9 your program should output 362880.");
          Console.WriteLine("Enter a whole number: ");
  
          numUserInput = Convert.ToInt32(Console.ReadLine());
          numAnswer = numUserInput;
  
          while (numAnswer > 1)
          {
              numAnswer -= 1;
              numUserInput = numUserInput * (numAnswer);
          }
  
          Console.WriteLine("Factorial is: " + numUserInput);
          Console.ReadLine();
  

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