diff --git a/ex18.c b/ex18.c
new file mode 100644
index 0000000..34bf3e1
--- /dev/null
+++ b/ex18.c
@@ -0,0 +1,108 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+#include <errno.h>
+#include <string.h>
+
+
+void die(const char *message)
+{
+    if(errno) {
+        perror(message);
+    } else {
+        printf("ERROR: %s\n", message);
+    }
+
+    exit(1);
+}
+
+
+typedef int (*compare_cb)(int a, int b);
+
+
+int *bubble_sort(int *numbers, int count, compare_cb cmp)
+{
+    int temp = 0;
+    int i = 0;
+    int j = 0;
+    int *target = malloc(count * sizeof(int));
+
+    if(!target) die("Memory error.");
+
+    memcpy(target, numbers, count * sizeof(int));
+
+    for(i = 0; i < count; i++) {
+        for(j = 0; j < count - 1; j++) {
+            if(cmp(target[j], target[j+1]) > 0) {
+                temp = target[j+1];
+                target[j+1] = target[j];
+                target[j] = temp;
+            }
+        }
+    }
+
+    return target;
+}
+
+
+int sorted_order(int a, int b)
+{
+    return a - b;
+}
+
+
+int reverse_order(int a, int b)
+{
+    return b - a;
+}
+
+
+int strange_order(int a, int b)
+{
+    if(a == 0 || b == 0) {
+        return 0;
+    } else {
+        return a % b;
+    }
+}
+
+
+void test_sorting(int *numbers, int count, compare_cb cmp)
+{
+    int i = 0;
+    int *sorted = bubble_sort(numbers, count, cmp);
+
+    if(!sorted) die("Failed to sort as requested.");
+
+    for(i = 0; i < count; i++) {
+        printf("%d ", sorted[i]);
+    }
+    printf("\n");
+
+    free(sorted);
+}
+
+
+int main(int argc, char *argv[])
+{
+    if(argc  < 2) die("USAGE: ex18 4 3 1 5 6");
+
+    int count = argc - 1;
+    int i = 0;
+    char **inputs = argv + 1;
+
+    int *numbers = malloc(count * sizeof(int));
+    if(!numbers) die("Memory error.");
+
+    for(i = 0; i < count; i++) {
+        numbers[i] = atoi(inputs[i]);
+    }
+
+    test_sorting(numbers, count, sorted_order);
+    test_sorting(numbers, count, reverse_order);
+    test_sorting(numbers, count, strange_order);
+
+    free(numbers);
+
+    return 0;
+}