Write a Factorial program in C using recursion

Write a Factorial program in C using recursion:

Program:-

    #include<stdio.h>
    
    long factorial(int);
    
    int main()
    {
      int n;
      long f;
    
      printf("Enter an integer to find its factorial\n");
      scanf("%d", &n);
    
      if (n < 0)
        printf("Factorial of negative integers isn't defined.\n");
      else
      {
        f = factorial(n);
        printf("%d! = %ld\n", n, f);
      }
    
      return 0;
    }
    
    long factorial(int n)
    {
      if (n == 0)
        return 1;
      else
        return(n * factorial(n-1));
    }