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I am trying to compile this program
I'm trying to compile this program, but the compiler is complaining that ``union REGS'' is undefined, and the linker is complaining that int86 is undefined. Those have to do with MS-DOS interrupt programming. They don't exist on other systems. 2015-03-02, 1489👍, 0💬

Why is this loop always executing once?
Why is this loop always executing once? for(i = start; i &lt; end; i++); { printf("%d\n", i); } A: The accidental extra semicolon hiding at the end of the line containing the for constitutes a null statement which is, as far as the compiler is concerned, the loop body. The following brace-enclos... 2015-06-03, 1488👍, 0💬

I am trying to take some square roots
I'm trying to take some square roots, and I've simplified the code down to main() { printf("%f\n", sqrt(144.)); } but I'm still getting crazy numbers. Make sure that you have #included &lt;math.h>, and correctly declared other functions returning double. (Another library function to be careful w... 2015-07-01, 1487👍, 0💬

Why isnt it being handled properly?
I'm reading strings typed by the user into an array, and then printing them out later. When the user types a sequence like \n, why isn't it being handled properly? Character sequences like \n are interpreted at compile time. When a backslash and an adjacent n appear in a character constant or string... 2015-08-24, 1486👍, 0💬

Once I have used freopen, how can I get the original stdout (or stdin) back?
Once I have used freopen, how can I get the original stdout (or stdin) back? There isn't a good way. If you need to switch back, the best solution is not to have used freopen in the first place. Try using your own explicit output (or input) stream variable, which you can reassign at will, while leav... 2015-10-01, 1485👍, 0💬

I thought I would check errno after a long string of printf calls ...
I thought I'd check errno after a long string of printf calls, to see if any of them had failed: errno = 0; printf("This\n"); printf("is\n"); printf("a\n"); printf("test.\n"); if(errno != 0) fprintf(stderr, "printf failed: %s\n", strerror(errno)); Why is it printing something strange like ``printf f... 2015-10-14, 1483👍, 0💬

I had a frustrating problem which turned out to be caused by the line
I had a frustrating problem which turned out to be caused by the line printf("%d", n); where n was actually a long int. I thought that ANSI function prototypes were supposed to guard against argument type mismatches like this. When a function accepts a variable number of arguments, its prototype doe... 2015-06-15, 1483👍, 0💬

How can I access an I O board directly?
How can I access an I O board directly? At one level, at least, it's quite simple: you have a device register which is actually wired up so that the bits written to it get coverted to actual voltage levels in the real world that you can do interesting things with. In general, there are two ways to g... 2015-04-20, 1483👍, 0💬

How can I get random integers in a certain range?
How can I get random integers in a certain range? The obvious way, rand() % N /* POOR */ (which tries to return numbers from 0 to N-1) is poor, because the low-order bits of many random number generators are distressingly non-random. A better method is something like (int)((double)rand() / ((double)... 2015-07-29, 1479👍, 0💬

Why isnt my procedure call working? The compiler seems to skip right over it
Why isnt my procedure call working? The compiler seems to skip right over it Does the code look like this? myprocedure; C has only functions, and function calls always require parenthesized argument lists, even if empty. Use myprocedure(); Without the parentheses, the reference to the function name ... 2015-06-01, 1479👍, 0💬

How can I allocate arrays or structures bigger than 64K?
How can I allocate arrays or structures bigger than 64K? A reasonable computer ought to give you transparent access to all available memory. If you're not so lucky, you'll either have to rethink your program's use of memory, or use various system-specific techniques. 64K is (still) a pretty big chun... 2015-03-30, 1478👍, 0💬

I am getting baffling syntax errors which make no sense at all
I'm getting baffling syntax errors which make no sense at all, and it seems like large chunks of my program aren't being compiled. Check for unclosed comments, mismatched #if/#ifdef/#ifndef/#else/#endi fdirectives, and perhaps unclosed quotes; remember to check header files, too. 2015-06-01, 1477👍, 0💬

How can I make it pause before closing the program output window?
I'm compiling some test programs on a windows-based system, and the windows containing my program's output are closing so quickly after my program calls exit that I can't see the output. How can I make it pause before closing? After wondering why the author of your compiler's run-time system didn't ... 2015-04-24, 1476👍, 0💬

How can I return multiple values from a function?
How can I return multiple values from a function? There are several ways of doing this. (These examples show hypothetical polar-to-rectangular coordinate conversion functions, which must return both an x and a y coordinate.) 1. Pass pointers to several locations which the function can fill in: #incl... 2015-02-25, 1476👍, 0💬

How can I read/write structures from/to data files?
How can I read/write structures from/to data files? It is relatively straightforward to write a structure out using fwrite: fwrite(&amp;somestruct, sizeof somestruct, 1, fp); and a corresponding fread invocation can read it back in. What happens here is that fwrite receives a pointer to the stru... 2015-09-18, 1475👍, 0💬

How can I read a binary data file properly?
How can I read a binary data file properly? I'm occasionally seeing 0x0a and 0x0d values getting garbled, and I seem to hit EOF prematurely if the data contains the value 0x1a. When you're reading a binary data file, you should specify "rb" mode when calling fopen, to make sure that text file transl... 2015-09-24, 1474👍, 0💬

How can I get the current date or time of day in a C program?
How can I get the current date or time of day in a C program? Just use the time, ctime, localtime and/or strftime functions. Here is a simple example: #include &lt;stdio.h> #include &lt;time.h> int main() { time_t now; time(&amp;now); printf("It's %s", ctime(&amp;now)); return 0; } C... 2015-08-07, 1472👍, 0💬

Why do all the lines end up containing copies of the last line?
I'm using fgets to read lines from a file into an array of pointers. Why do all the lines end up containing copies of the last line? You have only allocated memory for one line, linebuf. Each time you call fgets, the previous line is overwritten. fgets doesn't do any memory allocation: unless it rea... 2015-11-13, 1470👍, 0💬

How can I find the modification date and time of a file?
How can I find the modification date and time of a file? The Unix and POSIX function is stat, which several other systems supply as well. 2015-04-13, 1468👍, 0💬

How can my program discover the complete pathname to the executable from which it was invoked?
How can my program discover the complete pathname to the executable from which it was invoked? argv[0] may contain all or part of the pathname, or it may contain nothing. You may be able to duplicate the command language interpreter's search path logic to locate the executable if the name in argv[0]... 2015-03-13, 1467👍, 0💬

But I cant use all these nonstandard, system-dependent functions, because my program has to be ANSI compatible!
But I cant use all these nonstandard, system-dependent functions, because my program has to be ANSI compatible! You're out of luck. Either you misunderstood your requirement, or it's an impossible one to meet. ANSI/ISO Standard C simply does not define ways of doing these things; it is a language st... 2015-02-27, 1466👍, 0💬

A third-party header file I just started using is defining its own TRUE and FALSE values incompatibly ...
A third-party header file I just started using is defining its own TRUE and FALSE values incompatibly with the code I've already developed. What can I do? This is indeed an annoying situation. It's a classic namespace problem;Ideally, third-party vendors would be conscientious when defining symbols ... 2016-02-26, 1464👍, 0💬

How can I insert or delete a line (or record) in the middle of a file?
How can I insert or delete a line (or record) in the middle of a file? In general, there is no way to do this. The usual solution is simply to rewrite the file. When you find yourself needing to insert data into an existing file, here are a few alternatives you can try: * Rearrange the data file so ... 2015-10-05, 1464👍, 0💬

How can I return a sequence of random numbers which dont repeat at all?
How can I return a sequence of random numbers which dont repeat at all? What you're looking for is often called a ``random permutation'' or ``shuffle.'' One way is to initialize an array with the values to be shuffled, then randomly interchange each of the cells with another one later in the array: ... 2015-07-24, 1464👍, 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