diff --git a/.gitignore b/.gitignore
index 32d1ca3..a0dc815 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,5 +2,6 @@ python/__pycache__
 rust/*/Cargo.lock
 rust/*/target/*
 cpp/a.out
+cpp/*/*.o
 java/*/*.class
 scheme/*.so
diff --git a/cpp/append_digit_primes.cpp b/cpp/append_digit_primes.cpp
deleted file mode 100644
index b47e037..0000000
--- a/cpp/append_digit_primes.cpp
+++ /dev/null
@@ -1,107 +0,0 @@
-#include <iostream>
-#include <vector>
-#include <string>
-#include <unordered_map>
-
-using ull = unsigned long long;
-
-auto next(ull x) -> std::vector<ull>;
-auto is_prime(ull n) -> bool;
-
-class Tree
-{
-public:
-    ull value;
-    std::vector<Tree> children;
-
-    Tree(ull value, std::vector<ull> tree_children) : value(value) {
-        for (ull child : tree_children) {
-            children.push_back(Tree(child, {}));
-        }
-    }
-
-    void step() {
-        if (children.size() == 0) {
-            auto xs = next(value);
-            for (auto val : xs) {
-                children.push_back(Tree(val, {}));
-            }
-        } else {
-            for (auto &child : children) {
-                child.step();
-            }
-        }
-    }
-
-    auto longest_path() -> std::vector<ull> {
-        if (children.size() == 0) {
-            return { value };
-        }
-        std::vector<ull> max_path;
-        int max_length = 0;
-        for (auto &child : children) {
-            auto temp = child.longest_path();
-            if (temp.size() > max_length) {
-                max_length = temp.size();
-                max_path = temp;
-            }
-        }
-        std::vector<ull> retval = { value };
-        retval.insert(retval.end(), max_path.begin(), max_path.end());
-        return retval;
-    }
-};
-
-auto next(ull x) -> std::vector<ull> {
-    std::vector<ull> new_xs;
-    ull temp = x * 10;
-    for (int i = 0; i < 10; i++) {
-        auto temp2 = temp + i;
-        if (is_prime(temp2)) {
-            new_xs.push_back(temp2);
-        }
-    }
-    return new_xs;
-}
-
-auto is_prime(ull n) -> bool {
-    static std::unordered_map<ull, bool> primes;
-    if (n < 2) { 
-        primes[n] = false;
-        return false;
-    }
-    if (primes.count(n) > 0) {
-        return primes[n];
-    }
-    for (int i = 2; i * i <= n; i++) {
-        if (n % i == 0) {
-            primes[n] = false;
-            return false;
-        }
-    }
-    primes[n] = true;
-    return true;
-}
-
-template <typename T>
-auto print_vec(std::vector<T> vec) -> void {
-    std::cout << '[';
-    for (T &val : vec) {
-        std::cout << val << ", ";
-    }
-    std::cout << "]\n";
-}
-
-auto main() -> int {
-    /* std::vector<ull> primes; */
-    /* for (int i = 2; i < 10000000; i++) { */
-    /*     if (is_prime(i)) { */
-    /*         primes.push_back(i); */
-    /*     } */
-    /* } */
-    Tree tree(0, {});
-    for (int i = 0; i < 9; i++) {
-        tree.step();
-        print_vec(tree.longest_path());
-    }
-}
diff --git a/cpp/append_digit_primes/Makefile b/cpp/append_digit_primes/Makefile
new file mode 100644
index 0000000..e2cddb8
--- /dev/null
+++ b/cpp/append_digit_primes/Makefile
@@ -0,0 +1,23 @@
+# rename `template` to name of project
+TARGET=append_digit_primes
+CXX=g++
+OFILES=../common/tree.o ../common/util.o
+LIBS=
+CXXFLAGS=-g
+
+$(TARGET): $(OFILES) $(TARGET).o
+	$(CXX) $(CXXFLAGS) -o $@ $(TARGET).o $(OFILES) $(LIBS)
+
+%.o: %.cpp
+	$(CXX) $(CXXFLAGS) -c -o $@ $<
+
+PHONY: clean run all
+
+clean:
+	rm *.o $(TARGET)
+
+run:
+	./$(TARGET)
+
+all:
+	make $(TARGET)
diff --git a/cpp/append_digit_primes/append_digit_primes.cpp b/cpp/append_digit_primes/append_digit_primes.cpp
new file mode 100644
index 0000000..08600c6
--- /dev/null
+++ b/cpp/append_digit_primes/append_digit_primes.cpp
@@ -0,0 +1,28 @@
+#include "../common/util.h"
+#include "../common/tree.h"
+
+#include <cstdlib>
+
+auto next(ull x) -> std::vector<ull> {
+    std::vector<ull> new_xs;
+    ull temp = x * 10;
+    for (int i = 0; i < 10; i++) {
+        auto temp2 = temp + i;
+        if (is_prime(temp2)) {
+            new_xs.push_back(temp2);
+        }
+    }
+    return new_xs;
+}
+
+auto main(int argc, char *argv[]) -> int {
+    if (argc != 2) {
+        std::cout << "Usage: append_digit_primes <search_depth>\n";
+        return -1;
+    }
+    Tree tree(0, {});
+    for (int i = 0; i < std::atoi(argv[1]); i++) {
+        tree.step(next);
+        print_vec(tree.longest_path());
+    }
+}
diff --git a/cpp/common/tree.cpp b/cpp/common/tree.cpp
new file mode 100644
index 0000000..589addc
--- /dev/null
+++ b/cpp/common/tree.cpp
@@ -0,0 +1,41 @@
+#include "tree.h"
+
+/* all tree stuff, don't really need to change it unless you have some ideas for
+ * optimizations 
+ */
+Tree::Tree(ull value, std::vector<ull> tree_children) : value(value) {
+    for (ull child : tree_children) {
+        children.push_back(Tree(child, {}));
+    }
+}
+
+void Tree::step(std::vector<ull> (*next)(ull)) {
+    if (children.size() == 0) {
+        auto xs = next(value);
+        for (auto val : xs) {
+            children.push_back(Tree(val, {}));
+        }
+    } else {
+        for (auto &child : children) {
+            child.step(next);
+        }
+    }
+}
+
+auto Tree::longest_path() -> std::vector<ull> {
+    if (children.size() == 0) {
+        return { value };
+    }
+    std::vector<ull> max_path;
+    int max_length = 0;
+    for (auto &child : children) {
+        auto temp = child.longest_path();
+        if (temp.size() > max_length) {
+            max_length = temp.size();
+            max_path = temp;
+        }
+    }
+    std::vector<ull> retval = { value };
+    retval.insert(retval.end(), max_path.begin(), max_path.end());
+    return retval;
+}
diff --git a/cpp/common/tree.h b/cpp/common/tree.h
new file mode 100644
index 0000000..7f88c26
--- /dev/null
+++ b/cpp/common/tree.h
@@ -0,0 +1,17 @@
+#include <vector>
+
+using ull = unsigned long long;
+
+/* all tree stuff, don't really need to change it unless you have some ideas for
+ * optimizations 
+ */
+class Tree
+{
+public:
+    ull value;
+    std::vector<Tree> children;
+
+    Tree(ull value, std::vector<ull> tree_children);
+    void step(std::vector<ull> (*next)(ull));
+    auto longest_path() -> std::vector<ull>;
+};
diff --git a/cpp/common/util.cpp b/cpp/common/util.cpp
new file mode 100644
index 0000000..54b4e85
--- /dev/null
+++ b/cpp/common/util.cpp
@@ -0,0 +1,30 @@
+#include "util.h"
+
+/* some helper functions */
+auto is_prime(ull n) -> bool {
+    static std::unordered_map<ull, bool> primes;
+    if (n < 2) { 
+        primes[n] = false;
+        return false;
+    }
+    if (primes.count(n) > 0) {
+        return primes[n];
+    }
+    for (int i = 2; i * i <= n; i+=2) {
+        if (n % i == 0) {
+            primes[n] = false;
+            return false;
+        }
+        if (i == 2) i--;
+    }
+    primes[n] = true;
+    return true;
+}
+
+auto print_vec(std::vector<ull> vec) -> void {
+    std::cout << '[';
+    for (ull val : vec) {
+        std::cout << val << ", ";
+    }
+    std::cout << "]\n";
+}
diff --git a/cpp/common/util.h b/cpp/common/util.h
new file mode 100644
index 0000000..49b1d86
--- /dev/null
+++ b/cpp/common/util.h
@@ -0,0 +1,10 @@
+#include <vector>
+#include <unordered_map>
+#include <iostream>
+
+using ull = unsigned long long;
+
+/* some helper functions */
+auto is_prime(ull n) -> bool;
+
+auto print_vec(std::vector<ull> vec) -> void;
diff --git a/cpp/template.cpp b/cpp/template.cpp
deleted file mode 100644
index 9793c62..0000000
--- a/cpp/template.cpp
+++ /dev/null
@@ -1,104 +0,0 @@
-#include <iostream>
-#include <vector>
-#include <string>
-#include <unordered_map>
-
-using ull = unsigned long long;
-
-auto next(ull x) -> std::vector<ull>;
-auto is_prime(ull n) -> bool;
-
-/* all tree stuff, don't really need to change it unless you have some ideas for
- * optimizations 
- */
-class Tree
-{
-public:
-    ull value;
-    std::vector<Tree> children;
-
-    Tree(ull value, std::vector<ull> tree_children) : value(value) {
-        for (ull child : tree_children) {
-            children.push_back(Tree(child, {}));
-        }
-    }
-
-    void step() {
-        if (children.size() == 0) {
-            auto xs = next(value);
-            for (auto val : xs) {
-                children.push_back(Tree(val, {}));
-            }
-        } else {
-            for (auto &child : children) {
-                child.step();
-            }
-        }
-    }
-
-    auto longest_path() -> std::vector<ull> {
-        if (children.size() == 0) {
-            return { value };
-        }
-        std::vector<ull> max_path;
-        int max_length = 0;
-        for (auto &child : children) {
-            auto temp = child.longest_path();
-            if (temp.size() > max_length) {
-                max_length = temp.size();
-                max_path = temp;
-            }
-        }
-        std::vector<ull> retval = { value };
-        retval.insert(retval.end(), max_path.begin(), max_path.end());
-        return retval;
-    }
-};
-
-/* TODO Tweak this to change functionality according to explanation on the
- * Overleaf 
- */
-auto next(ull x) -> std::vector<ull> {
-    std::vector<ull> new_xs;
-    return new_xs;
-}
-
-/* some helper functions */
-auto is_prime(ull n) -> bool {
-    static std::unordered_map<ull, bool> primes;
-    if (n < 2) { 
-        primes[n] = false;
-        return false;
-    }
-    if (primes.count(n) > 0) {
-        return primes[n];
-    }
-    for (int i = 2; i * i <= n; i++) {
-        if (n % i == 0) {
-            primes[n] = false;
-            return false;
-        }
-    }
-    primes[n] = true;
-    return true;
-}
-
-template <typename T>
-auto print_vec(std::vector<T> vec) -> void {
-    std::cout << '[';
-    for (T &val : vec) {
-        std::cout << val << ", ";
-    }
-    std::cout << "]\n";
-}
-
-auto main() -> int {
-    /* starts off with a tree with value 0 and no children and searches 20
-     * iterations, feel free to tweak to whatever you want
-     */
-    Tree tree(0, {});
-    for (int i = 0; i < 20; i++) {
-        tree.step();
-        print_vec(tree.longest_path());
-    }
-}
diff --git a/cpp/template/Makefile b/cpp/template/Makefile
new file mode 100644
index 0000000..9456565
--- /dev/null
+++ b/cpp/template/Makefile
@@ -0,0 +1,23 @@
+# rename `template` to name of project
+TARGET=template
+CXX=g++
+OFILES=../common/tree.o ../common/util.o
+LIBS=
+CXXFLAGS=-g
+
+$(TARGET): $(OFILES) $(TARGET).o
+	$(CXX) $(CXXFLAGS) -o $@ $(TARGET).o $(OFILES) $(LIBS)
+
+%.o: %.cpp
+	$(CXX) $(CXXFLAGS) -c -o $@ $<
+
+PHONY: clean run all
+
+clean:
+	rm *.o $(TARGET)
+
+run:
+	./$(TARGET)
+
+all:
+	make $(TARGET)
diff --git a/cpp/template/template.cpp b/cpp/template/template.cpp
new file mode 100644
index 0000000..f0012e4
--- /dev/null
+++ b/cpp/template/template.cpp
@@ -0,0 +1,19 @@
+/* include little library I made */
+#include "../common/util.h"
+#include "../common/tree.h"
+
+auto next(ull x) -> std::vector<ull> {
+    std::vector<ull> new_xs;
+    return new_xs;
+}
+
+auto main() -> int {
+    /* starts off with a tree with value 0 and no children and searches 20
+     * iterations, feel free to tweak to whatever you want
+     */
+    Tree tree(0, {});
+    for (int i = 0; i < 20; i++) {
+        tree.step(next);
+        print_vec(tree.longest_path());
+    }
+}
diff --git a/python/append_digit_primes.py b/python/append_digit_primes.py
index 5add74d..4c85055 100644
--- a/python/append_digit_primes.py
+++ b/python/append_digit_primes.py
@@ -1,76 +1,21 @@
 import math
 
-class Tree:
-    def __init__(self, value, children):
-        self.value = value
-        self.children = []
-        for child in children:
-            self.children.append(Tree(child, []))
+from tree import Tree
+import util
 
-    def step(self):
-        if len(self.children) == 0:
-            for val in step(self.value):
-                self.children.append(Tree(val, []))
-            return
-        for child in self.children:
-            child.step()
-
-    def __str__(self):
-        retval = '[' + str(self.value) + ': '
-        for child in self.children:
-            retval += str(child)
-        retval += ']'
-        return retval
-
-    def __repr__(self):
-        return str(self)
-
-    def longest_path(self):
-        if len(self.children) == 0:
-            return [self.value]
-        max_path = []
-        max_length = 0
-        for child in self.children:
-            temp = child.longest_path()
-            if len(temp) > max_length:
-                max_path = temp
-                max_length = len(temp)
-        return [self.value] + max_path
-
-def is_square(x):
-    return int(math.sqrt(x)) == math.sqrt(x)
-
-primes = {}
-
-def is_prime(x):
-    try:
-        return primes[x]
-    except KeyError:
-        if x < 2:
-            primes[x] = False
-            return False
-        i = 2
-        while i * i <= x:
-            if x % i == 0:
-                primes[x] = False
-                return False
-            i += 1
-        primes[x] = True
-        return True
-
-def step(x):
+def next(x):
     new_xs = []
     for i in range(10):
-        if is_prime(10 * x + i):
+        if util.is_prime(10 * x + i):
             new_xs.append(10 * x + i)
     return new_xs
 
 
 def main():
     tree = Tree(0, [])
-    for i in range(9):
+    for i in range(20):
         print(tree.longest_path())
-        tree.step()
+        tree.step(next)
     print(tree.longest_path())
 
 
diff --git a/python/insert_digit_anywhere_primes.py b/python/insert_digit_anywhere_primes.py
index 7cf8cf3..c96b53e 100644
--- a/python/insert_digit_anywhere_primes.py
+++ b/python/insert_digit_anywhere_primes.py
@@ -1,68 +1,16 @@
 import math
 
-class Tree:
-    def __init__(self, value, children):
-        self.value = value
-        self.children = []
-        for child in children:
-            self.children.append(Tree(child, []))
+from tree import Tree
+import util
 
-    def step(self):
-        if len(self.children) == 0:
-            for val in step(self.value):
-                self.children.append(Tree(val, []))
-            return
-        for child in self.children:
-            child.step()
-
-    def __str__(self):
-        retval = '[' + str(self.value) + ': '
-        for child in self.children:
-            retval += str(child)
-        retval += ']'
-        return retval
-
-    def __repr__(self):
-        return str(self)
-
-    def longest_path(self):
-        if len(self.children) == 0:
-            return [self.value]
-        max_path = []
-        max_length = 0
-        for child in self.children:
-            temp = child.longest_path()
-            if len(temp) > max_length:
-                max_path = temp
-                max_length = len(temp)
-        return [self.value] + max_path
-
-def is_square(x):
-    return int(math.sqrt(x)) == math.sqrt(x)
-
-primes = {}
-
-def is_prime(x):
-    try:
-        return primes[x]
-    except KeyError:
-        i = 2
-        while i * i <= x:
-            if x % i == 0:
-                primes[x] = False
-                return False
-            i += 1
-        primes[x] = True
-        return True
-
-def step(x):
+def next(x):
     new_xs = []
     str_x = str(x)
     for (i,digit) in enumerate(str_x + '0'):
         for d in range(0,10):
             temp = str_x[:i] + str(d) + str_x[i:]
             if not (i == 0 and d == 0):
-                if is_prime(int(temp)):
+                if util.is_prime(int(temp)):
                     new_xs.append(int(temp))
     return new_xs
 
@@ -71,7 +19,7 @@ def main():
     tree = Tree(0, [2, 3, 5, 7])
     for i in range(5):
         print(tree.longest_path())
-        tree.step()
+        tree.step(next)
     print(tree.longest_path())
     print(tree)
 
diff --git a/python/insert_digit_anywhere_squares.py b/python/insert_digit_anywhere_squares.py
index 9b181cf..941dab1 100644
--- a/python/insert_digit_anywhere_squares.py
+++ b/python/insert_digit_anywhere_squares.py
@@ -1,53 +1,16 @@
 import math
 
-class Tree:
-    def __init__(self, value, children):
-        self.value = value
-        self.children = []
-        for child in children:
-            self.children.append(Tree(child, []))
+from tree import Tree
+import util
 
-    def step(self):
-        if len(self.children) == 0:
-            for val in step(self.value):
-                self.children.append(Tree(val, []))
-            return
-        for child in self.children:
-            child.step()
-
-    def __str__(self):
-        retval = '[' + str(self.value) + ': '
-        for child in self.children:
-            retval += str(child)
-        retval += ']'
-        return retval
-
-    def __repr__(self):
-        return str(self)
-
-    def longest_path(self):
-        if len(self.children) == 0:
-            return [self.value]
-        max_path = []
-        max_length = 0
-        for child in self.children:
-            temp = child.longest_path()
-            if len(temp) > max_length:
-                max_path = temp
-                max_length = len(temp)
-        return [self.value] + max_path
-
-def is_square(x):
-    return int(math.sqrt(x)) == math.sqrt(x)
-
-def step(x):
+def next(x):
     new_xs = []
     str_x = str(x)
     for (i,digit) in enumerate(str_x + '0'):
         for d in range(0,10):
             temp = str_x[:i] + str(d) + str_x[i:]
             if not (i == 0 and d == 0):
-                if is_square(int(temp)):
+                if util.is_square(int(temp)):
                     new_xs.append(int(temp))
     return new_xs
 
@@ -55,7 +18,7 @@ def step(x):
 def main():
     tree = Tree(0, [1,4,9])
     for i in range(20):
-        tree.step()
+        tree.step(next)
     print(tree)
     print(tree.longest_path())
 
diff --git a/python/template.py b/python/template.py
index 91a54e5..d740478 100644
--- a/python/template.py
+++ b/python/template.py
@@ -1,65 +1,8 @@
 import math
 
-# tree stuff, I wouldn't recommend tweaking unless you have serious ideas for
-# optimizations
-class Tree:
-    def __init__(self, value, children):
-        self.value = value
-        self.children = []
-        for child in children:
-            self.children.append(Tree(child, []))
-
-    def step(self):
-        if len(self.children) == 0:
-            for val in next(self.value):
-                self.children.append(Tree(val, []))
-            return
-        for child in self.children:
-            child.step()
-
-    def __str__(self):
-        retval = '[' + str(self.value) + ': '
-        for child in self.children:
-            retval += str(child)
-        retval += ']'
-        return retval
-
-    def __repr__(self):
-        return str(self)
-
-    def longest_path(self):
-        if len(self.children) == 0:
-            return [self.value]
-        max_path = []
-        max_length = 0
-        for child in self.children:
-            temp = child.longest_path()
-            if len(temp) > max_length:
-                max_path = temp
-                max_length = len(temp)
-        return [self.value] + max_path
-
-# some utility functions, same as above
-def is_square(x):
-    return int(math.sqrt(x)) == math.sqrt(x)
-
-primes = {}
-
-def is_prime(x):
-    try:
-        return primes[x]
-    except KeyError:
-        if x < 2:
-            primes[x] = False
-            return False
-        i = 2
-        while i * i <= x:
-            if x % i == 0:
-                primes[x] = False
-                return False
-            i += 1
-        primes[x] = True
-        return True
+# these are the tree and utility libraries I created
+from tree import Tree
+import util
 
 # TODO: tweak this to do whatever you want as I described in the Overleaf
 def next(x):
@@ -72,7 +15,7 @@ def main():
     tree = Tree(0, [])
     for i in range(20):
         print(tree.longest_path())
-        tree.step()
+        tree.step(next)
     print(tree.longest_path())
 
 
diff --git a/python/tree.py b/python/tree.py
new file mode 100644
index 0000000..133c23b
--- /dev/null
+++ b/python/tree.py
@@ -0,0 +1,40 @@
+import math
+
+# tree stuff, I wouldn't recommend tweaking unless you have serious ideas for
+# optimizations
+class Tree:
+    def __init__(self, value, children):
+        self.value = value
+        self.children = []
+        for child in children:
+            self.children.append(Tree(child, []))
+
+    def step(self, next):
+        if len(self.children) == 0:
+            for val in next(self.value):
+                self.children.append(Tree(val, []))
+            return
+        for child in self.children:
+            child.step(next)
+
+    def __str__(self):
+        retval = '[' + str(self.value) + ': '
+        for child in self.children:
+            retval += str(child)
+        retval += ']'
+        return retval
+
+    def __repr__(self):
+        return str(self)
+
+    def longest_path(self):
+        if len(self.children) == 0:
+            return [self.value]
+        max_path = []
+        max_length = 0
+        for child in self.children:
+            temp = child.longest_path()
+            if len(temp) > max_length:
+                max_path = temp
+                max_length = len(temp)
+        return [self.value] + max_path
diff --git a/python/util.py b/python/util.py
new file mode 100644
index 0000000..e1b79eb
--- /dev/null
+++ b/python/util.py
@@ -0,0 +1,23 @@
+import math
+
+# some utility functions, same as above
+def is_square(x):
+    return int(math.sqrt(x)) == math.sqrt(x)
+
+primes = {}
+
+def is_prime(x):
+    try:
+        return primes[x]
+    except KeyError:
+        if x < 2:
+            primes[x] = False
+            return False
+        i = 2
+        while i * i <= x:
+            if x % i == 0:
+                primes[x] = False
+                return False
+            i += 1
+        primes[x] = True
+        return True