main: Add default char set

Previously the user was required to specify a custom char set, or the
upwgen exited with an error. Now it assumes ascii 33 - 126, which
include all english lower case, upper case, numbers, and some symbols by
default (which is sane since this is what most password fields accept).

Also updated README to document this default.

2 files changed, 8 insertions, 5 deletions

diff --git a/README.adoc b/README.adoc
index eb6abc0..0e846f0 100644
--- a/README.adoc
+++ b/README.adoc
@@ -8,6 +8,10 @@ terminal font. Regardless, most softwares offer font fallback to render the
 maximum number of characters possible. Even if your font cannot render the
 characters, copy and paste will probably still work.
 
+The default character set selected if no custom set is specified is ASCII 33 -
+126, or English lower case, upper case, numbers, and some symbols (if a
+standard US keyboard can type it, it is in this default group).
+
 Usage
 -----
 
diff --git a/src/main.c b/src/main.c
index c1836be..1f048ed 100644
--- a/src/main.c
+++ b/src/main.c
@@ -169,11 +169,10 @@ int main(int argc, char* argv[]) {
     i++;
   }
 
-  // Ensure at least one character set was specified
-  if(chars[0] == '\0') {
-    printf("Must specify at least one character set\n");
-    return 0;
-  }
+  // If no charset was specified, use standard ascii 33 - 126 chars, which
+  // includes english lower case, upper case, numbers, and some symbols.
+  if(chars[0] == '\0')
+    count += intrcat(chars, 33, 126);
 
   // Get the random data seed
   clock_gettime(CLOCK_REALTIME, &ts);