message: Added a check for tabs
  Whitespace can be of any type - space or tabs.
diff: @@ -12,8 +12,8 @@ public:
  int sign = 1;
  int i = 0;
  - // Skip ' '.
  - while (str[i] == ' ') {
  + // Skip whitespace.
  + while (str[i] == ' ' || str[i] == '\t') {
  ++i;
  }
  