calculate Factorial function added

src/calculateFactorial.c

@@ -0,0 +1,19 @@
+
+
+#include "calculateFactorial.h"
+
+int calculateFactorial_integer(int n) {
+    if (n < 0) {
+
+    } else if (n == 0 || n == 1) {
+
+        return 1;
+    } else {
+
+        int result = 1;
+        for (int i = 2; i <= n; ++i) {
+            result *= i;
+        }
+        return result;
+    }
+}

src/calculateFactorial.h

@@ -0,0 +1,8 @@
+
+
+#ifndef THEADMIRALS_CALCULATEFACTORIAL_H
+#define THEADMIRALS_CALCULATEFACTORIAL_H
+
+int calculateFactorial_integer(int n);
+
+#endif //THEADMIRALS_CALCULATEFACTORIAL_H