Check out example codes for "factorial in c++". It will help you in understanding the concepts better.

Code Example 1

#include<bits/stdc++.h>
#include<stdio.h>
using namespace std;

int fact(int i){
	if (i <= 1) return 1;
  	else return i*fact(i-1);
}

int main(){
  	ios::sync_with_stdio(0);
  	cin.tie(0);
  	int N;
  	cin >> N;
  	cout << fact(N) << "\n";
  	return 0;
}

Code Example 2

#include <cmath>

int fact(int n){
    return std::tgamma(n + 1);  
}    
// for n = 5 -> 5 * 4 * 3 * 2 = 120 
//tgamma performas factorial with n - 1 -> hence we use n + 1

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