My C code is not responding after scanf statement

cscanf

I have wrote a set of code that scan in values and use them to test out central limit theorem. However when I run my program after I input all the values using scanf my program is not proceeding to the next lines of code : the problem looks like this:

printf("*** DEMONSTRATION OF CENTRAL LIMIT THEOREM ***");
printf("Enter parameters for the distribution [a b]    ==> ");
scanf("%f %f",&a,&b);
printf("Enter distribution to display [1=data, 2=mean] ==> ");
scanf("%d",&option);
printf("Enter number in each group                     ==> ");
scanf("%d",&group);
printf("Enter number of samples of groups              ==> ");
scanf("%f",&times);
printf("are we here yet");

after these printf and scanf the program starts to do the calculations. But When I run the program after I compile(successfully). It seems my code is stuck after the scanf("%f",&times);

the line "are we here yet" never gets printed, meaning the program did not get past the scanf. I have not done much C programming this seemed really strange to me can someone figure out why the program is not excuting past the line scanf("%f",&times); I really appericate it

Best Answer

Input/output at the terminal is line-buffered in C, and output is not going to display until you output a newline character, or you call fflush(stdout), or your program terminates normally and all the buffers are flushed anyway. Change:

printf("are we here yet");

to:

printf("are we here yet\n");

or:

printf("are we here yet");
fflush(stdout);

and you should see your output.

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Sqlite – Improve INSERT-per-second performance of SQLite

Several tips:

Put inserts/updates in a transaction.
For older versions of SQLite - Consider a less paranoid journal mode (pragma journal_mode). There is NORMAL, and then there is OFF, which can significantly increase insert speed if you're not too worried about the database possibly getting corrupted if the OS crashes. If your application crashes the data should be fine. Note that in newer versions, the OFF/MEMORY settings are not safe for application level crashes.
Playing with page sizes makes a difference as well (PRAGMA page_size). Having larger page sizes can make reads and writes go a bit faster as larger pages are held in memory. Note that more memory will be used for your database.
If you have indices, consider calling CREATE INDEX after doing all your inserts. This is significantly faster than creating the index and then doing your inserts.
You have to be quite careful if you have concurrent access to SQLite, as the whole database is locked when writes are done, and although multiple readers are possible, writes will be locked out. This has been improved somewhat with the addition of a WAL in newer SQLite versions.
Take advantage of saving space...smaller databases go faster. For instance, if you have key value pairs, try making the key an INTEGER PRIMARY KEY if possible, which will replace the implied unique row number column in the table.
If you are using multiple threads, you can try using the shared page cache, which will allow loaded pages to be shared between threads, which can avoid expensive I/O calls.
Don't use !feof(file)!

I've also asked similar questions here and here.

Why is scanf() causing infinite loop in this code

scanf consumes only the input that matches the format string, returning the number of characters consumed. Any character that doesn't match the format string causes it to stop scanning and leaves the invalid character still in the buffer. As others said, you still need to flush the invalid character out of the buffer before you proceed. This is a pretty dirty fix, but it will remove the offending characters from the output.

char c = '0';
if (scanf("%d", &number) == 0) {
  printf("Err. . .\n");
  do {
    c = getchar();
  }
  while (!isdigit(c));
  ungetc(c, stdin);
  //consume non-numeric chars from buffer
}

edit: fixed the code to remove all non-numeric chars in one go. Won't print out multiple "Errs" for each non-numeric char anymore.

Here is a pretty good overview of scanf.

Best Answer

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Sqlite – Improve INSERT-per-second performance of SQLite

Why is scanf() causing infinite loop in this code

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