--- /dev/null
+#if !defined(_gcd_H)
+# define _gcd_H (1)
+
+/*Computes the gcd of two integers, _a and _b.
+ _a: The first integer of which to compute the gcd.
+ _b: The second integer of which to compute the gcd.
+ Return: The non-negative gcd of _a and _b.
+ If _a and _b are both 0, then 0 is returned, though in reality the
+ gcd is undefined, as any integer, no matter how large, will divide 0
+ evenly.*/
+int gcd(int _a,int _b);
+
+#endif