Update homework 1 and 2

examples/hw1/gcd.c

@@ -0,0 +1,15 @@
+int gcd(int a, int b) {
+    a = (a > 0) ? a : -a;
+    b = (b > 0) ? b : -b;
+
+    while(a != b) {
+        if(a > b) { a -= b; }
+        else { b -= a; }
+    }
+
+    return a;
+}
+
+int main() {
+    return gcd(18, 21) == 3;
+}