Why does this simple C command line tool always exit without working?

Question

I've just typed in an example from K&R...

#include <stdio.h>

int main (int argc, const char * argv[]) {

    int c, nl;

    nl = 0;

    while ((c = getchar()) != EOF) {

        if (c == '\n') {
            ++nl;   
        }



    }

    printf("new lines=> %d\n", nl);

    return 0;
}

However, when I build & run, I get...

minimac:~ alex$ /Users/alex/Documents/K\&R/build/Debug/K\&R ; exit;

As you may be able to gather, running off the Mac OS X Terminal, if that means anything.

Why doesn't this ever prompt for input?

Update

Here is how I started my project, on Mac OS X Snow Leopard

• Ran Xcode
• Started new project "command line tool" and called it K&R
• Typed in the code into main.c
• Hit the big button above "build & run"
• Double clicked K&R and Terminal was launched with the output above

I might also state that I have been using interpreted languages pretty much my entire life, so I am new to this compiling process.

When I use gcc to compile from the Terminal, I can run the program with ./a.out. However, once I type, I don't know how to tell the program I'm done, now please tell me how many lines have I typed in.

Here is a screenshot of my Terminal...

Answer 1

Looks like you are doing this in Xcode. Not sure how Xcode handles stdin/out and what project template you are using. You should have all this in a simple .c file and just gcc it yourself without Xcode and see what happens then.

Edit: in Unix console, you press Ctrl-D to end stdin input to a command line program. Wikipedia has more.

Answer 2

OK, I just did what you said in your steps, and I am able to type into the terminal. However, before I get to see the output from the program, the terminal is closed (because of the exit;). I added a #include <unistd.h> at the beginning and sleep(2); right before return 0;, and I can see the correct output.

Here is the complete program:

#include <stdio.h>
#include <unistd.h>

int main (int argc, const char * argv[]) {

    int c, nl;

    nl = 0;

    while ((c = getchar()) != EOF) {

        if (c == '\n') {
            ++nl;   
        }



    }

    printf("new lines=> %d\n", nl);
    sleep(2);

    return 0;
}