C++ exercise problem

**Pantheon** · 09-04-2006

I've been working on a programming exercise and have run into a problem at the end. The goal is to write a program that outputs the number of each lower case letter in the programs own source file in a 2 column table using only 2 char variables and one int. Here is my code.

Code:

#include <iostream>
#include <fstream>
using namespace std;


ifstream instream;

int main ()
{
for (char aval = 97; aval <= 122; aval++)
{
int count = 0;
char b;
instream.open("ASCII.cpp");
while (!instream.eof())
	{
	instream.get(b);
		if (aval == b)
		{
		count++;
		}
	}
cout << aval << " " << count << "\n";
instream.close();
}
return 0;
}

Yet when I run it I get a column of letter (as expected) but the second column only shows 0's after the first letter. I think it might have something to do with the scoping of the count variable, but I can't pin the problem down, any help is appreciated.

**dwks** · 09-04-2006

Code:

while (!instream.eof())

You shouldn't do this, it's like !feof(). Check the return value of get() instead.

You need to clear the eof flag for insteam, or re-declare the variable. A fix would be:

Code:

ifstream instream.open("ASCII.cpp");
while (!instream.eof())

Or:

Code:

instream.clear();
instream.open("ASCII.cpp");
while (!instream.eof())

I think it's clear(), anyway.

**Hikaru** · 09-04-2006

Reading the file completely for every letter is really inefficient. You can use a map instead to store all of the letters and counts by reading the file just one time.

Code:

#include <cctype>
#include <fstream>
#include <iostream>
#include <map>

int main()
{
    std::ifstream is(__FILE__);

    if (is)
    {
        typedef std::map<char, int> letterMap;

        letterMap letters;
        char ch;

        while (is.get(ch))
        {
            if (std::islower(ch))
            {
                ++letters[ch];
            }
        }

        letterMap::iterator iter;

        for (iter = letters.begin(); iter != letters.end(); ++iter)
        {
            std::cout << iter->first << ": " << iter->second << "\n";
        }
    }

    return 0;
}

**Cat** · 09-04-2006

In addition, I think reading the entire file 26 times to accomplish the task is overkill.

Consider making an array of 26 integers, one for each letter.

Here's some very rough code to get you started:

Code:

int count[26];

// initialize all 26 members to zero (you need a for loop)


char b;
while(instream.get(b)){
   if (b >= 'a' && b <= 'z')
      count[b - 'a'] ++;
}

// Then loop through all the letters and print
for (char c = 'a', c <= 'z', c++){

}

There are other ways to do this, including std::vector or std::map.

I'd also recommend losing the "using namespace std" and just prefixing std:: in the two places you'd need it. It's a better habit to get into.

Edit: got beaten to the punch.

**twomers** · 09-04-2006

But these are limitations which the OP has to abide by. ... using only 2 char variables and one int

**dwks** · 09-04-2006

. . . and one ifstream object.

**Cat** · 09-04-2006

Ah. In that case I still wouldn't open and close the file 26 times, I'd open it once, and when get() returned an error, clear() and seekg(0) to get back to the beginning of the file for reading again.

**jafet** · 09-05-2006

One... variable! Yeah, I seriously need a life.

Code:

#include <iterator>
#include <algorithm>
#include <fstream>
#include <iostream>

int main(char c)
{
	if(c < 'a') c = 'a';
	std::ifstream i("file.txt");
	std::cout << c << " "
		<< std::count(std::istream_iterator <char> (i), std::istream_iterator <char> (), c)
		<< "\n";
	if(c == 'z')
	{
		return 0;
	}
	return main(c+1);
}

**Rennor** · 09-05-2006

Originally Posted by jafet

One... variable! Yeah, I seriously need a life.

No wonder I love to read this forum

**Salem** · 09-05-2006

You've got to wonder what all these "teachers" are thinking to achieve with "can you solve this problem in 'x'" type questions.
Interesting diversions they may be for experienced programmers, but no way to be teaching newbies how to program.

Just how many rules has jafet broken?
- wrong prototype for main
- recursive call to main

**achy1729** · 09-05-2006

In my computer its working fine, except for the fact that it isn't displaying the 'a's and 'b's

**Pantheon** · 09-06-2006

I agree, the stipulations on this problem seem a bit arbitrary, completeing the task with an array was no problem, but that would be too correct to be right. Thanks everyone for the advice, everything is working fine now.

**jafet** · 09-07-2006

- Implicitly assuming the high-order byte of argc will be less than 'a'
- Implicitly assuming successful opening of file
- ...
Maybe I should try Lisp. It might suit my style better.

About the assignment; perhaps the class is for embedded software developers? One can only wonder...

**dwks** · 09-07-2006

All those problems with jafet's code (that I can see) could be fixed by using a separate function to do the recursion.

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