Why does program not execute final printf statement?

Question

I cannot figure out why program control does not reach the third printf, right after the for loop.

Why won't the third printf print?

If I change the for loop to while loop, it still will not print.

Here is the program and output:

main()
{
    double nc;

    printf ("Why does this work, nc = %f\n", nc);
    for (nc = 0; getchar() != EOF; ++nc)
    {
        printf ("%.0f\n", nc);
    }
    printf ("Why does this work, nc = %f", nc);
}

The output is:

Why does this work, nc = 0.000000
test
0
1
2
3
4

this may answer your question: stackoverflow.com/a/1716621/748875 — Simon
– Simon, Commented Jun 30, 2012 at 22:15
Out of interest: why double for nc? Surely an int would be more traditional? — LeoNerd
– LeoNerd, Commented Jul 2, 2012 at 10:56

Levon · Accepted Answer · 2012-06-30 23:04:17Z

4

It works fine for me, how are you trying to termintate the program? The for-loop should end once EOF is detected as input by getchar().

EOF is Control-Z (^Z) under Windows and Control-D (^D) under Linux/Unix. Once I enter this, the loop terminates and I get the final printf() to display its output.

As a final note (as mentioned by @DanielFisher too), add a '\n' at the end of your final printf() call as it may be required by your particular implementation or otherwise the program's behavior might be undefined (thanks to @KeithThompson and @AndreyT pointing this out in the comments):

 printf ("Why does this work, nc = %f\n", nc);

edited Jun 30, 2012 at 23:04

answered Jun 30, 2012 at 21:29

Levon

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8 Comments

Keith Thompson Over a year ago

The trailing \n isn't just stylistic. It's implementation-defined whether a trailing '\n' is required. If it is required, failing to provide one makes the program's behavior undefined.

Levon Over a year ago

@KeithThompson Interesting, could you elaborate on this requirement, I hadn't heard about this before. Does it have to do with whether it causes the output buffer to be flushed?

AnT stands with Russia Over a year ago

@Levon: The language specification states in 7.19.2/2 with regard to text streams: "Whether the last line requires a terminating new-line character is implementation-defined."

Levon Over a year ago

Why the downvote? I'd be happy to improve the answer or correct any errors, but It's not useful to OP, SO or me without an explanation.

Levon Over a year ago

@AndreyT Thanks .. I just found it and read up on it. Eliminated all references to stylistic :)

|

Simon · Accepted Answer · 2012-06-30 21:59:07Z

0

printf is buffered, that's why the final line may not be displayed. That means a call to printf may not result in a direct output as the function accumulates data before putting it in the output (your terminal).

A call to fflush after your last printf will put everything that remains in the buffer in your terminal. Also, the buffer is flushed every time you ask for a newline.

answered Jun 30, 2012 at 21:59

Simon

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