Use of recursion

include<iostream>
using namespace std;

int factorial( int n)
{   if(n<2)
  {    return 1;       }
    int prvsnmbr=factorial(n-1);
   
   
      return n*factorial(n-1);
    }
int sum(int n)
{    if (n<1)
      {return 0;}
      return (n+sum(n-1));
               }
           
  int fibonacciseries(int n)
{     if(n==1)
          { return 1;}
        if(n==0)
        { return 0;}
     int prevsnmbr = fibonacciseries(n-1)+fibonacciseries(n-2);
   
        return  prevsnmbr;}         
int main()
{   int n;
cout <<"Enter the number = ";
  cin>>n;
cout<<"factorial of nmbr = "<<factorial(n)<<endl;
cout <<"sum oh nth nmbr = "<<sum(n)<<endl;
  cout<<"fibonacciseries of nmbr= "<<fibonacciseries(n)<<endl;
 
    return 0;
}