better document GCD programs

math/gcd_iterative_euclidean.cpp

@@ -1,10 +1,17 @@
-#include <cmath>
+/**
+ * @file
+ * @brief Compute the greatest common denominator of two integers using
+ * *iterative form* of
+ * [Euclidean algorithm](https://en.wikipedia.org/wiki/Euclidean_algorithm)
+ *
+ * @see gcd_recursive_euclidean.cpp
+ */
 #include <iostream>
 #include <stdexcept>
 
-// will find the greatest common denominator of two ints integers
-// Euclidean algorithm can be found here
-// https://en.wikipedia.org/wiki/Euclidean_algorithm
+/**
+ * algorithm
+ */
 int gcd(int num1, int num2) {
     if (num1 <= 0 | num2 <= 0) {
         throw std::domain_error("Euclidean algorithm domain is for ints > 0");
@@ -34,6 +41,9 @@ int gcd(int num1, int num2) {
     return previous_remainder;
 }
 
+/**
+ * Main function
+ */
 int main() {
     std::cout << "gcd of 120,7 is " << (gcd(120, 7)) << std::endl;
     try {

math/gcd_recursive_euclidean.cpp

@@ -0,0 +1,48 @@
+/**
+ * @file
+ * @brief Compute the greatest common denominator of two integers using
+ * *recursive form* of
+ * [Euclidean algorithm](https://en.wikipedia.org/wiki/Euclidean_algorithm)
+ *
+ * @see gcd_iterative_euclidean.cpp
+ */
+#include <iostream>
+
+/**
+ * algorithm
+ */
+int gcd(int num1, int num2) {
+    if (num1 <= 0 | num2 <= 0) {
+        throw std::domain_error("Euclidean algorithm domain is for ints > 0");
+    }
+
+    if (num1 == num2) {
+        return num1;
+    }
+
+    // Everything divides 0
+    if (num1 == 0) return num2;
+    if (num2 == 0) return num1;
+
+    // base case
+    if (num1 == num2) return num1;
+
+    // a is greater
+    if (num1 > num2) return gcd(num1 - num2, num2);
+    return gcd(num1, num2 - num1);
+}
+
+/**
+ * Main function
+ */
+int main() {
+    std::cout << "gcd of 120,7 is " << (gcd(120, 7)) << std::endl;
+    try {
+        std::cout << "gcd of -120,10 is " << gcd(-120, 10) << std::endl;
+    } catch (const std::domain_error &e) {
+        std::cout << "Error handling was successful" << std::endl;
+    }
+    std::cout << "gcd of 312,221 is " << (gcd(312, 221)) << std::endl;
+    std::cout << "gcd of 289,204 is " << (gcd(289, 204)) << std::endl;
+    return 0;
+}

math/greatest_common_divisor.cpp

@@ -1,27 +0,0 @@
-// C++ program to find GCD of two numbers
-#include <iostream>
-
-// Recursive function to return gcd of a and b
-int gcd(int a, int b) {
-    // Everything divides 0
-    if (a == 0)
-       return b;
-    if (b == 0)
-       return a;
-
-    // base case
-    if (a == b)
-        return a;
-
-    // a is greater
-    if (a > b)
-        return gcd(a-b, b);
-    return gcd(a, b-a);
-}
-
-// Driver program to test above function
-int main() {
-    int a = 98, b = 56;
-    std::cout << "GCD of " << a << " and " << b << " is " << gcd(a, b);
-    return 0;
-}