add trick example of greatest-common-divisor, knuth-morris-pratt, primality-test, quick-pow, split-text

trick/greatest-common-divisor.cpp

@@ -0,0 +1,8 @@
+int greatest_common_divisor(int num1, int num2) {
+	while (num2 != 0) {
+		int temp = num2;
+		num2 = num1 % num2;
+		num1 = temp;
+	}
+	return num1;
+}