Reformat and document c/isogram

c/isogram/src/isogram.c

@@ -3,14 +3,12 @@
 
 int length(const char string[]) {
   int i = 0;
-  while (string[i] != '\0') {
-    i++;
-  }
-  return i+1; // Account for terminating null character.
+  while (string[i] != '\0') { i++; }
+  return i+1; // Account for terminating null char.
 }
 
 char lowercase(char c) {
-  // Lowercase only ASCII capital characters.
+  // Lowercase only ASCII uppercase chars.
   if (c >= 65 && c <= 90) {
     return c + 32;
   }
@@ -18,11 +16,11 @@ char lowercase(char c) {
 }
 
 bool is_symbol_char(char c) {
-  // Ignore symbols that precede alpha chars.
+  // Catch chars that precede or follow alpha chars.
   if (c < 65 || c > 122) {
     return true;
   }
-  // Ignore symbols intervening the upper and lowercase chars.
+  // Catch chars intervening the upper and lowercase alpha chars.
   if (c > 90 && c < 97) {
     return true;
   }
@@ -32,14 +30,13 @@ bool is_symbol_char(char c) {
 bool is_isogram(const char phrase[]) {
   if (phrase == NULL) { return false; }
   if (length(phrase) == 0) { return true; }
-  // There are 26 lowercased ASCII alpha chars.
+  // There are 26 lowercased ASCII alpha chars (97-122).
   // We can use 26 indexes to keep track of each one.
   char char_map[26] = { 0 };
   for (int i = 0; i < length(phrase); i++) {
     if (is_symbol_char(phrase[i])) { continue; } // Ignore non-alpha chars.
-    if (char_map[lowercase(phrase[i]) - 97] != 0) {
-      return false;
-    }
+    if (char_map[lowercase(phrase[i]) - 97] != 0) { return false; }
+    // Keep track of chars by incrementing the index value.
     char_map[lowercase(phrase[i]) - 97]++;
   }
   return true;