Easier way to write this if function c++

Question

is there an easier way to write this if statement?

int main ()
{
  char k[100];
  int i=0;
  ifstream fd ("info.txt");
  while (!in.eof())
  {
    fd >> k[i]
    if (int(k[i]) != 96 || int(k[i]) != 97 || 
        int(k[i]) != 98 || int(k[i]) != 99)
            i++;
  } 
}

and so on till 122. Basically all I want to do is check if the symbol in the .txt file matches all the alphabet letters, @ sign and a " . " (period)

Is there an easier way to do all of this? Any help is much appreciated !

Use `isalpha` and check for the specific symbols? Also, do not use magic numbers. If you want to check for `a` use `'a'` not some number. — NathanOliver, Oct 10 '16 at 16:42
also, see [why is `iostream::eof` inside a loop condition condsidered wrong?](http://stackoverflow.com/questions/5605125/why-is-iostreameof-inside-a-loop-condition-considered-wrong). Also, [this question](http://stackoverflow.com/q/39150884/4892076) on testing whether a character matches a set of characters. — jaggedSpire, Oct 10 '16 at 16:44
This isn't your actual code. I doubt your compiler didn't complain about the undefined `in` symbol. — StoryTeller - Unslander Monica, Oct 10 '16 at 16:45
BTW, the `@` sign has [ASCII table value](http://www.asciitable.com/) of 64, not 96. — Thomas Matthews, Oct 10 '16 at 16:51

score 4 · Accepted Answer · edited May 23 '17 at 12:16

Try this:

char c;
while (fd >> c)
{
  if ((c < '`') || (c > 'c'))
  {
    k[i] = c;
    ++i;
  }
}

Usually, using character constants is more readable than their ASCII decimal equivalents.

Also, using eof in a loop is considered wrong, so place the input operation in the while expression.

Since your values are contiguous, you can use the < and > operators to reduce the number of comparisons.

Edit 1:
Another alternative is to place the valid letters into a string and search the string.

const std::string invalid_letters = "@.abcdefghijklmnopqrstuvwxyz";
while (fd >> c)
{
  if (invalid_letters.find(c) == std::string::npos)
  {
    k[i] = c;
    ++i;
  }
}

You can also use islower to detect lowercase letters.

Character constants are usually more *portable* than codepoints, too. Although that's not the case here, because something is assumed about their ordering... — Toby Speight, Oct 10 '16 at 17:01

score 0 · Answer 2 · answered Oct 10 '16 at 16:49

0

You can write your if statement like this:

    if (int(k[i]) < 96 || int(k[i]) > 122){
        i++;
    }

answered Oct 10 '16 at 16:49

SpiralDev

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score 0 · Answer 3 · answered Oct 10 '16 at 16:54

int countemailchars(istream & is)
{
   char ch;
   int answer = 0;
   while(is.get(&ch))
   {
      if(strchr("abcdefghijklmnopqrstuvwxyz.@", tolower(ch)))
         answer++;
   }

   return answer;
}

ifstream fd ("info.txt");
int N = countemailchars(fd);

Easier way to write this if function c++

3 Answers3