searching strings for certain letters...why is for loop not looping through all letters of string?

Question

I have a file of a bunch of words and want to extract the ones that contain a 'q' or 'Q'. I have a function called isQWord that scans a string for these letters and, if it does contain these letters, puts the word into a vector called qwords. The function also does a few other things, but I've omitted these parts because they don't pertain to the issue. Then, in my main function, I use isQWord to read all the strings from my file. Here is my code:

bool isQWord(string str); // return true if str contains a 'q' or 'Q'

ifstream inFile;
vector<string> qwords;

int main() {

  string str;
  inFile.open("DictionaryLarge.txt");
  
  while(!inFile.eof()) { // go through contents of DictionaryLarge.txt
    inFile >> str;
    isQWord(str); // call isQWord function on file contents
  }

  inFile.close();
  outFile.close();
  
}


bool isQWord(string str) {
   
   /* This function does three things:
   1. scans a string for 'q' or 'Q'
   2. appends q-words to the qwords vector
   3. finds the largest q-word and stores all q-words before this word to an output file
   */
 
    
  for(int x=0; x < str.size(); x++) { // read string
    
    if(str.at(x) == 'q' || str.at(x) == 'Q') { // append to qwords vector for q-words
      qwords.push_back(str);
      return true;
    }
    
    else if(str.size()==0) { // return false for blanks
      return false;
    }
        
    else { // return false for non q-words
      return false;
    }
    
  }
}

However, the for loop in isQWord is "stuck", so to speak, at my starting value of x = 0 and only returning words that begin with 'q' or 'Q' only. That is, it's reading something like if(str.at(0) == 'q' || str.at(0) == 'Q') and completely bypassing the for loop.

I've also instead tried a while loop like this:

  int i=0;
  while(str.size() != 0) {
    if(str.at(i) == 'q' || str.at(i) == 'Q') {
      qwords.push_back(str);
      break;
    }
    
    i++;
  }

but this throws an error in my main function when I try to call isQWord on my file contents. I'm hoping to stick with the for loop because I think this is closer to working.

Also, I realize there are certain library functions I could be using that would make this easier, but this is a homework assignment and I'm only allowed to use .size() and .at() to search for 'q's and 'Q's.

Thank you for any guidance.

Answer 1

Inside your isQWord() function, you are breaking your for loop after the first iteration no matter whether the rest of the word contains a Q or not. You are not scanning that entire string. You need to move the return false statement after the loop ends without finding a Q.

You are putting too much responsibility on the function. It should simply return whether the word has a Q or not, nothing more. Let the caller decide what it do with the word based on the return value of the function.

Also, your use of inFile.eof() is just plain wrong. See Why is iostream::eof inside a loop condition (i.e. `while (!stream.eof())`) considered wrong?.

Try this instead:

bool isQWord(const string &str);

int main() {
  ifstream inFile;
  vector<string> qwords;

  string str;
  inFile.open("DictionaryLarge.txt");
  
  while (inFile >> str) {
    if (isQWord(str)) {
      qwords.push_back(str);
    }
  }

  return 0;
}


bool isQWord(const string &str) {
  for(size_t x = 0; x < str.size(); ++x) {
    if (str[x] == 'q' || str[x] == 'Q') {
      return true;
    }
  }
  return false;
}