I see some things that may help you improve your code.
using namespace std
using namespace std at the top of every program is a bad habit that you'd do well to avoid. In my own production code, I usually simply type
std:: where needed. It's a little bit more typing but it has two very nice benefits: it absolutely avoids any possibility of name collisions and it makes it absolutely clear which particular namespace is being used for various items.
Make sure you have all required
The code uses
std::isalpha but doesn't
#include <cctype> or
<locale>. It's not clear which one you want here. The functions in
<cctype> match the functions you're using, but you should be aware that they are only defined for the
C locale. Read this for details.
Omit unused variables
word is never used, it can and should be omitted from the program.
Use better naming
I would say that
words is a good variable name, but
line (singular) is not. Also, we have
countletters (plural) but
countnum (singular). Some consistency in naming would improve this program.
Initialize and open files in one step
Instead of separately invoking
lab3.open() I'd suggest instead writing it this way:
Or if you wanted to make the program much more flexible and allow the user to specify a file name, this could be:
Decompose the program into smaller parts
Right now, all of the code is in
main which isn't necessarily wrong, it means that it's not only hard to reuse but also hard to troubleshoot. Better is to separate the code into small chunks. It makes it both easier to understand and easier to fix or improve. In this case, I'd suggest creating an object that looks like this:
void count(std::istream &in);
friend std::ostream& operator<<(std::ostream &out, const WordCounter &w);
When you define those functions, then, the
main routine can look like this:
std::cout << "Could not open file\n";
std::cout << counter;
Use consistent formatting
Using consistent formatting helps readers of your code understand it without distraction. This code is mostly well formatted, but the indenting within the
while loop is a bit inconsistent.
Use precise terminology
The code claims to be counting sentences, but is actually counting lines. Either number will work if no lines contain more than one sentence, but I did not see any guarantee that this will always be the case.
std::endl if you don't really need it
The difference betweeen
'\n' is that
'\n' just emits a newline character, while
std::endl actually flushes the stream. This can be time-consuming in a program with a lot of I/O and is rarely actually needed. It's best to only use
std::endl when you have some good reason to flush the stream and it's not very often needed for simple programs such as this one. Avoiding the habit of using
'\n' will do will pay dividends in the future as you write more complex programs with more I/O and where performance needs to be maximized.
When a C or C++ program reaches the end of
main the compiler will automatically generate code to return 0, so there is no need to put
return 0; explicitly at the end of
Note: when I make this suggestion, it's almost invariably followed by one of two kinds of comments: "I didn't know that." or "That's bad advice!" My rationale is that it's safe and useful to rely on compiler behavior explicitly supported by the standard. For C, since C99; see ISO/IEC 9899:1999 section 188.8.131.52.3:
[...] a return from the initial call to the
main function is equivalent to calling the
exit function with the value returned by the
main function as its argument; reaching the
} that terminates the
main function returns a value of 0.
For C++, since the first standard in 1998; see ISO/IEC 14882:1998 section 3.6.1:
If control reaches the end of main without encountering a return statement, the effect is that of executing return 0;
All versions of both standards since then (C99 and C++98) have maintained the same idea. We rely on automatically generated member functions in C++, and few people write explicit
return; statements at the end of a
void function. Reasons against omitting seem to boil down to "it looks weird". If, like me, you're curious about the rationale for the change to the C standard read this question. Also note that in the early 1990s this was considered "sloppy practice" because it was undefined behavior (although widely supported) at the time.
So I advocate omitting it; others disagree (often vehemently!) In any case, if you encounter code that omits it, you'll know that it's explicitly supported by the standard and you'll know what it means.