Question

/* stringlength
 * input: str, pointer to a string
 * output: integer representing the length of string str, 
 * not counting the terminating character.
 *
 * You may NOT call ANY functions within this function.
 */
int stringlength(char *str)
{
    // count the number of characters in str
  int count=0,k;
  for (k=0; str[k] != '\0';k++)
    count++;
    return count;
}

/* countchars
 * inputs: character c, string str
 * output:  The number of instances of c in the string str
 * You may not call ANY function calls within this function.
 */
int countchars(char c, char *str)
{
    // count the number of times c is found in str
  int k,count=0;
  for (k=0;str[k]=='\0';k++)
    {
      if (str[k] == c)
    count++;
      else;
    }

    return count;
}

/* countlines
 * input: char *filename - string containing the filename
 * output: integer representing the number of lines in the file
 */
int countlines(char *filename)
{
    // count the number of lines in the file called filename
  FILE *f = fopen(filename,"r");
    char ch;
    int lines=0;
  f = fopen(filename,"r");

  do{
    ch = fgetc(f);
    if( ch == '\n')
      lines++;
  }while( ch != EOF );

return lines;
}

I need help with these three different functions that I am implementing in my program. I am a beginner so go easy on me, the countlines function is giving me the most trouble. If anyone could explain why not or why these functions will work, it would be greatly appreciated.

Answer 1

There are a number of problems in countlines():

1. You open the file twice, but overwrite the first FILE * value with the second, so there’s no way you can close it. This is a minor problem.

2. The major problem is that the function fgetc() returns an int, not a char. In particular, EOF is a value different from every char.

3. The code does not close the file before returning. Generally, if you open a file in a function, then you should close it. If you don’t, you have to pass the file pointer back to the calling code so that it can close it.

4. The do ... while loop is seldom correct for an input loop (a while loop testing at the top is almost always much cleaner and clearer) but at least you weren’t using feof().

   int countlines(char *filename)
   {
       FILE *fp = fopen(filename,"r");
       int ch;
       int lines = 0;
       if (fp == 0)
           return lines;
   
       while ((ch = fgetc(fp)) != EOF)
       {
           if (ch == '\n')
               lines++;
       }
   
       fclose(fp);
   
       return lines;
   }
   

When you use char instead, one of two things happens:

• If your char type is signed, then a real character (often ÿ — y-umlaut, U+00FF, LATIN SMALL LETTER Y WITH DIAERESIS) also matches EOF so you can stop reading before you reach end of file.
• If your char type is unsigned, no value will ever match EOF so the loop will never stop.

---

In stringlength(), you have two variables count and k that are carefully kept at the same value; you only need one of the two.

---

Apart from raggedy indentation (endemic in the code shown — and definitely something to be avoided), and the unnecessary and pointless else; which does absolutely nothing, the code for countchars() looks OK (late addition) … has the condition in the for loop inverted; it should be str[k] != '\0', of course.