I added algorithm to find factorial of a number

Math/factorial.cpp

@@ -0,0 +1,18 @@
+#include<iostream>
+using namespace std;
+
+int main()
+{
+    int n;
+    cout<<"Enter number = ";
+    cin>>n;
+    int num=1;
+    for(int i=1;i<n;i++)
+    {
+        num*=i;
+    }
+    cout<<"Factorial of number is = ";
+    cout<<num<<endl;
+
+    return 0;
+}