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When I read numbers from the keyboard with scanf ...
When I read numbers from the keyboard with scanf and a "%d\n" format, like this: int n; scanf("%d\n", &amp;n); printf("you typed %d\n", n); it seems to hang until I type one extra line of input. Perhaps surprisingly, \n in a scanf format string does not mean to expect a newline, but rather to re... 2015-10-23, 1561👍, 0💬

How can I generate random numbers with a normal or Gaussian distribution?
How can I generate random numbers with a normal or Gaussian distribution? There are a number of ways of doing this. 1. Exploit the Central Limit Theorem (``law of large numbers'') and add up several uniformly-distributed random numbers: #include &lt;stdlib.h> #include &lt;math.h> #define NSU... 2015-07-22, 1561👍, 0💬

What does it mean when the linker says that _end is undefined?
What does it mean when the linker says that _end is undefined? That message is a quirk of the old Unix linkers. You get an error about _end being undefined only when other symbols are undefined, too--fix the others, and the error about _end will disappear. 2015-07-06, 1559👍, 0💬

I have got this tricky preprocessing I want to do and I cant figure out a way to do it.
I have got this tricky preprocessing I want to do and I cant figure out a way to do it. C's preprocessor is not intended as a general-purpose tool. (Note also that it is not guaranteed to be available as a separate program.) Rather than forcing it to do something inappropriate, you might want to wri... 2016-01-19, 1557👍, 0💬

Why do some versions of toupper act strangely if given an upper-case letter?
Why do some versions of toupper act strangely if given an upper-case letter? Why does some code call islower before toupper? In earlier times, toupper was a function-like preprocessor macro and was defined to work only on lower-case letters; it misbehaved if applied to digits, punctuation, or letter... 2015-08-17, 1557👍, 0💬

If I can say... why can't I say...
If I can say char a[] = "Hello, world!"; why can't I say char a[14]; Strings are arrays, and you can't assign arrays directly. Use strcpy instead: strcpy(a, "Hello, world!"); 2016-03-11, 1556👍, 0💬

How can I increase the allowable number of simultaneously open files?
I'm getting an error, ``Too many open files''. How can I increase the allowable number of simultaneously open files? A: There are typically at least two resource limitations on the number of simultaneously open files: the number of low-level ``file descriptors'' or ``file handles'' available in the ... 2015-04-03, 1556👍, 0💬

What's the difference between...?
What's the difference between #include &lt;> and #include "" ? The syntax is typically used with Standard or system-supplied headers, while "" is typically used for a program's own header files. 2016-02-16, 1554👍, 0💬

Where can I get an ANSI-compatible lint?
Where can I get an ANSI-compatible lint? Products called PC-Lint and FlexeLint are available from Gimpel Software. The Unix System V release 4 lint is ANSI-compatible, and is available separately (bundled with other C tools) from UNIX Support Labs or from System V resellers. Another ANSI-compatible ... 2015-05-05, 1552👍, 0💬

I need a sort of an approximate strcmp routine ...
I need a sort of an approximate strcmp routine ... Q: I need a sort of an ``approximate'' strcmp routine, for comparing two strings for close, but not necessarily exact, equality. A:Some nice information and algorithms having to do with approximate string matching, as well as a useful bibliography, ... 2015-01-09, 1552👍, 0💬

When I set a float variable to, say, 3.1, why is printf printing it as 3.0999999?
When I set a float variable to, say, 3.1, why is printf printing it as 3.0999999? Most computers use base 2 for floating-point numbers as well as for integers, and just as for base 10, not all fractions are representable exactly in base 2. It's well-known that in base 10, a fraction like 1/3 = 0.333... 2015-07-03, 1551👍, 0💬

I think somethings wrong with my compiler ...
I think something's wrong with my compiler: I just noticed that sizeof('a') is 2, not 1 (i.e. not sizeof(char)). Perhaps surprisingly, character constants in C are of type int, so sizeof('a') is sizeof(int) (though this is another area where C++ differs). 2016-03-04, 1550👍, 0💬

How can I handle floating-point exceptions gracefully?
How can I handle floating-point exceptions gracefully? On many systems, you can define a function matherr which will be called when there are certain floating-point errors, such as errors in the math routines in &lt;math.h>. You may also be able to use signal to catch SIGFPE 2015-03-04, 1549👍, 0💬

If fflush wont work, what can I use to flush input?
If fflush wont work, what can I use to flush input? It depends on what you're trying to do. If you're trying to get rid of an unread newline or other unexpected input after calling scanf you really need to rewrite or replace the call to scanf. Alternatively, you can consume the rest of a partially-r... 2015-10-12, 1545👍, 0💬

How can a process change an environment variable in its caller?
How can a process change an environment variable in its caller? It may or may not be possible to do so at all. Different operating systems implement global name/value functionality similar to the Unix environment in different ways. Whether the ``environment'' can be usefully altered by a running pro... 2015-03-11, 1545👍, 0💬

How can I invoke another program (a standalone executable, or an operating system command) from within a C program?
How can I invoke another program (a standalone executable, or an operating system command) from within a C program? Use the library function system, which does exactly that. Some systems also provide a family of spawn routines which accomplish approximately the same thing. system is more ``portable'... 2015-03-18, 1544👍, 0💬

How do I create a directory? How do I remove a directory (and its contents)?
How do I create a directory? How do I remove a directory (and its contents)? If your operating system supports these services, they are likely to be provided in C via functions named mkdir and rmdir. Removing a directory's contents as well will require listing them and calling remove . If you don't ... 2015-04-01, 1543👍, 0💬

I am trying to define a few simple little function-like macros ...
I'm trying to define a few simple little function-like macros such as #define square(x) x * x but they're not always working. There are three important rules to remember when defining function-like macros: 1. The macro expansion must always be parenthesized to protect any lower-precedence operators ... 2016-02-26, 1541👍, 0💬

Why does this code crash?
Why does this code: char *p = "hello, world!"; p[0] = 'H'; crash? String constants are in fact constant. The compiler may place them in nonwritable storage, and it is therefore not safe to modify them. When you need writable strings, you must allocate writable memory for them, either by declaring an... 2015-05-27, 1540👍, 0💬

Which is more efficient, a switch statement or an if else chain?
Which is more efficient, a switch statement or an if else chain? The differences, if any, are likely to be slight. The switch statement was designed to be efficiently implementable, though the compiler may choose to use the equivalent of an if/else chain (as opposed to a compact jump table) if the c... 2015-02-04, 1539👍, 0💬

I cant get va_arg to pull in an argument of type pointer-to-function.
I cant get va_arg to pull in an argument of type pointer-to-function. Try using a typedef for the function pointer type. The type-rewriting games which the va_arg macro typically plays are stymied by overly-complicated types such as pointer-to-function. To illustrate, a simplified implementation of ... 2015-06-05, 1538👍, 0💬

How can I swap two values without using a temporary?
How can I swap two values without using a temporary? The standard hoary old assembly language programmer's trick is: a ^= b; b ^= a; a ^= b; But this sort of code has little place in modern, HLL programming. Temporary variables are essentially free, and the idiomatic code using three assignments, na... 2015-02-06, 1533👍, 0💬

What are pragmas and what are they good for?
What are pragmas and what are they good for? The #pragma directive provides a single, well-defined ``escape hatch'' which can be used for all sorts of (nonportable) implementation-specific controls and extensions: source listing control, structure packing, warning suppression (like lint's old /* NOT... 2015-12-11, 1532👍, 0💬

If NULL and 0 are equivalent as null pointer constants, which should I use?
If NULL and 0 are equivalent as null pointer constants, which should I use? Many programmers believe that NULL should be used in all pointer contexts, as a reminder that the value is to be thought of as a pointer. Others feel that the confusion surrounding NULL and 0 is only compounded by hiding 0 b... 2015-05-11, 1532👍, 0💬

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.NET C C++ CSS DBA General HTML Java JavaScript JSP JUnit MySQL Networking Oracle Perl Perl PHP PL/SQL RSS Software QA SQL Server Struts Unix Windows XHTML XML