#include<iostream>
#include<stdio.h>

using namespace std;

int input[5]= {5,3,4,2,1};
int output[25],visited[5];

void permutation(int level,int takenElement,int totalArrayElement);
void printPermutaion(int takenElement);

int main()
{
    for(int t=0;t<5;t++)
    {
        permutation(0,t,5);
    }
    return 0;
}

void permutation(int level,int takenElement,int totalArrayElement)
{
    if(level == takenElement)
    {
        printPermutaion(takenElement);
        return;
    }

    for(int i=0;i<totalArrayElement;i++)
    {
        if(!visited[i])
        {
            visited[i] = true;
            output[level] = input[i];
            permutation(level+1,takenElement,totalArrayElement);
            visited[i] = false;
        }
    }
}

void printPermutaion(int takenElement)
{
    for(int i=0;i<takenElement;i++)
    {
        cout << output[i] << " " ;
    }

    cout << endl;
}

What is recursion? 

1. Base Case: if ( actualResult() == 2 ) result = a + b;
2. "Work toward base case": a+b becomes the first parameter
   This reduces the number of parameters to the function from 3 to 2, and 2 is the base case!
3. Recursive Call: add_numbers(a+b, c);

#include
using namespace std;

long long factorial(int num);

int main(void)
{
    int test_case;
    int T;
    int num;
    long long value;

    freopen("CreateRecursion.txt", "r", stdin);
    cin >> T;
    for (test_case = 1; test_case <= T; ++test_case)
    {
        scanf("%d", &num);
        value = factorial(num);
        printf("#%d %d! = %lld\n", test_case, num, value);
    }
}

long long factorial(int num)
{
    if (num == 0)
    {
        return 1;
    }
    else
    {
        return num * factorial(num - 1);
    }
}