diff --git a/chap1/double.c b/chap1/double.c
index 78d6e41..2778cd7 100644
--- a/chap1/double.c
+++ b/chap1/double.c
@@ -2,10 +2,12 @@
 #include <stdlib.h>
 #include <errno.h>
 #include <ctype.h>
+#include <string.h>
 
 int linenum;
 
 int getword(FILE *, char *, int);
+void doubleword(char *, FILE *);
 
 int main(int argc, char *argv[]) {
     int i;
@@ -27,6 +29,7 @@ int main(int argc, char *argv[]) {
     return EXIT_SUCCESS;
 }
 
+// getword reads a word from fp into buf, returning true if it was able to do so.
 int getword(FILE *fp, char *buf, int size) {
     int c;
     c = getc(fp);
@@ -50,3 +53,20 @@ int getword(FILE *fp, char *buf, int size) {
         ungetc(c, fp);
     return  buf[0] != '\0';
 }
+
+void doubleword(char *name, FILE *fp) {
+  char prev[128], word[128];
+
+  linenum = 1;
+  prev[0] = '\0';
+  while (getword(fp, word, sizeof word)) {
+    if (isalpha(word[0]) && strcmp(prev, word) == 0)
+      // word is a duplicate
+      {
+        if (name)
+          printf("%s:", name);
+        printf("%d: %s\n", linenum, word);
+      }
+    strcpy(prev, word);
+  }
+}
diff --git a/chap1/example.txt b/chap1/example.txt
new file mode 100644
index 0000000..6a9dba2
--- /dev/null
+++ b/chap1/example.txt
@@ -0,0 +1,3 @@
+hey there
+it's been a very very long
+time since
diff --git a/chap1/main b/chap1/main
new file mode 100755
index 0000000..1829119
Binary files /dev/null and b/chap1/main differ