diff --git a/histogram.cpp b/histogram.cpp
new file mode 100644
index 0000000..4d33c05
--- /dev/null
+++ b/histogram.cpp
@@ -0,0 +1,50 @@
+#include "histogram.h"
+
+using namespace std;
+
+static void
+find_minmax(const vector<double>& numbers, double& min, double& max)
+{
+    min = numbers[0];
+    max = numbers[0];
+    for (double x : numbers)
+    {
+        if (x > max )
+        {
+            max = x;
+        }
+        if (x < min)
+        {
+            min = x;
+        }
+    }
+}
+
+vector<size_t>
+make_histogram(const vector<double>& numbers, size_t& bin_count)
+{
+    double min = 0;
+    double max = 0;
+    find_minmax(numbers, min, max);
+    auto bin_size = (max - min)/bin_count;
+    vector<size_t> bins(bin_count);
+    for (double number : numbers)
+    {
+        bool found = false;
+        for (size_t j = 0; (j < bin_count - 1) && !found; j++)
+        {
+            auto lo = min + j * bin_size;
+            auto hi = min + (j + 1) * bin_size;
+            if ((lo <= number) && (number < hi))
+            {
+                bins[j]++;
+                found = true;
+            }
+        }
+        if (!found)
+        {
+            bins[bin_count - 1]++;
+        }
+    }
+    return bins;
+}
diff --git a/histogram.h b/histogram.h
new file mode 100644
index 0000000..cb3c148
--- /dev/null
+++ b/histogram.h
@@ -0,0 +1,9 @@
+#ifndef HISTOGRAM_H_INCLUDED
+#define HISTOGRAM_H_INCLUDED
+
+#include <vector>
+
+std::vector<size_t>
+make_histogram(const std::vector<double>& numbers, size_t& bin_count);
+
+#endif // HISTOGRAM_H_INCLUDED
diff --git a/main.cpp b/main.cpp
index 985134d..c3bc083 100644
--- a/main.cpp
+++ b/main.cpp
@@ -1,5 +1,6 @@
 #include <iostream>
 #include <vector>
+#include "histogram.h"
 
 using namespace std;
 
@@ -26,53 +27,6 @@ input_data()
     return in;
 }
 
-void
-find_minmax(const vector<double>& numbers, double& min, double& max)
-{
-    min = numbers[0];
-    max = numbers[0];
-    for (double x : numbers)
-    {
-        if (x > max )
-        {
-            max = x;
-        }
-        if (x < min)
-        {
-            min = x;
-        }
-    }
-}
-
-vector<size_t>
-make_histogram(const vector<double>& numbers, size_t& bin_count)
-{
-    double min = 0;
-    double max = 0;
-    find_minmax(numbers, min, max);
-    auto bin_size = (max - min)/bin_count;
-    vector<size_t> bins(bin_count);
-    for (double number : numbers)
-    {
-        bool found = false;
-        for (size_t j = 0; (j < bin_count - 1) && !found; j++)
-        {
-            auto lo = min + j * bin_size;
-            auto hi = min + (j + 1) * bin_size;
-            if ((lo <= number) && (number < hi))
-            {
-                bins[j]++;
-                found = true;
-            }
-        }
-        if (!found)
-        {
-            bins[bin_count - 1]++;
-        }
-    }
-    return bins;
-}
-
 void
 show_histogram_text(const vector<size_t>& bins, size_t& bin_count) {
     const size_t SCREEN_WIDTH = 80;