#include <iostream>
using namespace std;
void recurse(int input) //the recurse function...
{
     if (input == 0){ //if the input becomes 0, exit
               return;
               }
     recurse(input - 1); //calls itself
}
int main()
{
    int input;
 
    cout<<"Input a number to find the factorial of:\n";
    cin>>input; //get input value
    cin.get();
 
    recurse (input); //calls recurse function
    cout<<input * (input-1)<<"\n"; //multiplies it all together
    cin.get();
}

#include <iostream>
 
int sumFunction(int a, int b) {
     return a + b;
}
 
int main() {
     int a = 5, b = 7, c = 0;
     c = sumFunction(a, b); // c now is 5 + 7 = 12
     b = a + sumFunction(a, c); // b now is 5 + (5 + 12) = 22;
     std:cout << "123 + 123 = " << sumFunction(123, 123) << std::endl;
     return EXIT_SUCCESS;
}

int factorial(int n) {
     if(n==0) {
          return 1; // 0! = 1
     }
     return /* I leave it up to you what to return here. Hint: it should contain a call to factorial(int n) itself (hence recursion) */
}

 
int iReturn = recurse (input);
 
or 
 
int iReturn = 0;
 
iReturn = recurse (input);

#include <iostream>
using namespace std;
 
int factorial(int x);
 
int main(){
    int x;
 
    cout<<"Input a number to find the factorial of:\n";
    cin >> x;
    cin.ignore();
 
    cout<<"The factorial of " << x << " is " << factorial(x) << "\n";
    cin.get();
}
int factorial(int x){ 
    if (x == 0){
          return 1;
          }
    return x * factorial(x - 1); //it took me MONTHS to get THIS?!?!
}