program won't run properly

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The following code is from the recent edition of C++ Primer by Lippman

#include <iostream>
using std::cin;
using std::cout;
using std::endl;


int main()
{
    char ch;
    // initialize counters for each vowel
    int aCnt = 0, eCnt = 0, iCnt = 0, 
        oCnt = 0, uCnt = 0;

    while (cin>>ch ) {
    	// if ch is a vowel, increment the appropriate counter
    	switch (ch) {
    		case 'a':
    			++aCnt;
    			break;
    		case 'e':
            
    			++eCnt;
    			break;
    		case 'i':
            
    			++iCnt;
    			break;
    		case 'o':
            
    			++oCnt;
    			break;
    		case 'u':
                 
    			++uCnt;
    			break;
    	}
    }
    // print results
    cout << "Number of vowel a: \t" << aCnt << '\n'
         << "Number of vowel e: \t" << eCnt << '\n'
         << "Number of vowel i: \t" << iCnt << '\n'
         << "Number of vowel o: \t" << oCnt << '\n'
         << "Number of vowel u: \t" << uCnt << endl;
        system("pause");
    return 0;</iostream>

It shows its results extremly poorly. I can't make it read files. Other times
upon running, I type in characters and hit ^z then it shows after a long pause.
How can I make it work properly.

Posted 9-Jun-11 12:40pm

Petr_Kropotkin

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Albert Holguin 9-Jun-11 19:51pm

how are you trying to make it read files?

1 solution

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Sergey Alexandrovich Kryukov · Answer 1 · 2011-06-09T13:23:00

Solution 1

The while loop has no exit condition.

"How can I make it work properly?" — well, it depends what do you mean "properly". If you want, add a condition for exit right after line with while, such as

C++

while (cin>>ch ) {
   if (ch == 'q') break;
   switch (ch) {
      //...
   }
}

in this case the loop will exit on 'q' ("quit").

—SA

Posted 9-Jun-11 13:23pm

Sergey Alexandrovich Kryukov

Updated 12-Jun-11 12:36pm

v4

Comments

TRK3 9-Jun-11 19:54pm

Actually, while (cin>>ch) is the canonical way to scan an input until an error (including EOF) is encountered -- so it should work.

But personnally, I've never been fond of the C++ streams. For reading characters, I would always go with the tried and true C funtion: getchar() and test for EOF.

Albert Holguin 9-Jun-11 21:03pm

cin is the standard input, which if default from the prompt, not from file... if OP doesn't have code to redefine cin, its going to be the default.

TRK3 10-Jun-11 12:26pm

Depends on how he is invoking it. Could be invoking it from the command line with:

myprogram.exe < file.txt

Albert Holguin 13-Jun-11 13:34pm

true

psych00range 14-Jun-11 0:02am

i doubt hes invoking using commandline just on the knowledge that he has....it is always easier to have an exit condition for loops as debugging tool especially if your a beginner programmer

Sergey Alexandrovich Kryukov 14-Jun-11 1:18am

Huh?