Add hamming distance function

ex06/main.c

@@ -0,0 +1,28 @@
+#include "utils.h"
+#include <ctype.h>
+#include <stdio.h>
+#include <string.h>
+
+int main(int argc, char *argv[]) {
+  if (argc < 2) {
+    printf("Usage: %s <filename>\n", argv[0]);
+    return EXIT_FAILURE;
+  }
+
+  const char *filename = argv[1];
+
+  FILE *fp = fopen(filename, "r");
+  if (fp == NULL) {
+    printf("Error opening file %s\n", filename);
+    return EXIT_FAILURE;
+  }
+
+  printf("%u\n", hamming("this is a test", "wokka wokka!!!"));
+
+  if (fclose(fp)) {
+    printf("Error closing file %s\n", filename);
+    return EXIT_FAILURE;
+  }
+
+  return EXIT_SUCCESS;
+}