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Function Calls
What will be printed as the result of the operation below: #define swap(a,b) a=a+b;b=a-b;a=a-b; void main() { int x=5, y=10; swap (x,y); printf("%d %d\n",x,y); swap2(x,y); printf("%d %d\n",x,y); } int swap2(int a, int b) { int temp; temp=a; b=a; a=temp; return 0; } The correct answer is 10, 5 5, 10 2007-02-26, 7226👍, 0💬

Overriding Defined Macros
How do you override a defined macro? You can use the #undef preprocessor directive to undefine (override) a previously defined macro. 2007-02-26, 7138👍, 0💬

Multi-dimension Arrays
Write down the equivalent pointer expression for referring the same element a[i][j][k][l]? a[i] == *(a+i) a[i][j] == *(*(a+i)+j) a[i][j][k] == *(*(*(a+i)+j)+k) a[i][j][k][l] == *(*(*(*(a+i)+j)+k)+l) 2007-02-26, 7137👍, 0💬

Determing the Size of Allocated Memory Blocks
How can you determine the size of an allocated portion of memory? You can't, really. free() can , but there's no way for your program to know the trick free() uses. Even if you disassemble the library and discover the trick, there’s no guarantee the trick won’t change with the next release of the co... 2007-02-26, 7093👍, 0💬

Calling Base Class Methods
How can method defined in multiple base classes with same name be invoked from derived class simultaneously? class x { public: m1(); }; class y { public: m1(); }; class z: public x, public y { public: m1() { x::m1(); y::m1(); } }; 2007-02-26, 7065👍, 0💬

Variable Types
What are the types of variables x, y, y and u defined in the following code? #define Atype int* typedef int *p; p x, z; Atype y, u; Answer: x and z are pointers to int. y is a pointer to int but u is just an integer variable 2007-02-26, 7045👍, 0💬

Determining If Symbols Are Defined or Not
How can you check to see whether a symbol is defined? You can use the #ifdef and #ifndef preprocessor directives to check whether a symbol has been defined (#ifdef) or whether it has not been defined (#ifndef). Can you define which header file to include at compile time? Yes. This can be done by usi... 2007-02-26, 6870👍, 0💬

Opening Files to Share with Other Programs
How can I open a file so that other programs can update it at the same time? Your C compiler library contains a low-level file function called sopen() that can be used to open a file in shared mode. Beginning with DOS 3.0, files could be opened in shared mode by loading a special program named SHARE... 2007-02-26, 6859👍, 0💬

Shift Operations
What will the following piece of code do? int f(unsigned int x) { int i; for (i=0; x!=0; x&gt;&gt;1) { if (x &amp; 0x1) i++; } return i; } Answer: returns the number of ones in the input parameter X. 2007-02-26, 6771👍, 0💬

Swapping Variables
Can you write a program to interchange 2 variables without using the third one? a = 7; b = 2; a = a + b; b = a - b; a = a - b; 2007-02-26, 6747👍, 0💬

C question
What is the difference between: myObj *x = new myObj[100]; delete x; and myObj *x = new myObj[100]; delete [] x; 2009-07-16, 5547👍, 0💬

How can i trap the arrow keys inside the timer program?
How can i trap the arrow keys inside the timer program? How do you trap arrow keys in a regular program? What makes a timer program special? 2009-04-19, 4989👍, 0💬

About listing of the process
how to write a .c program in unix ,like I want to list the process information when I give the process id. 2010-04-07, 4403👍, 0💬

How can I convert numbers to strings (the opposite of atoi)? Is there an itoa function?
How can I convert numbers to strings (the opposite of atoi)? Is there an itoa function? Just use sprintf: sprintf(string, "%d", number); (Don't worry that sprintf may be overkill, potentially wasting run time or code space; it works well in practice.) You can obviously use sprintf to convert long or... 2015-08-24, 3452👍, 0💬

In a call to malloc, what does an error like
In a call to malloc, what does an error like ``Cannot convert `void *' to `int *''' mean? It means you're using a C++ compiler instead of a C compiler. 2016-06-21, 3077👍, 0💬

I see code like ...
I see code like char *p = malloc(strlen(s) + 1); strcpy(p, s); Shouldn't that be malloc((strlen(s) + 1) * sizeof(char))? It's never necessary to multiply by sizeof(char), since sizeof(char) is, by definition, exactly 1. (On the other hand, multiplying by sizeof(char) doesn't hurt, and in some circum... 2016-06-21, 2735👍, 0💬

What is the difference between fgetpos/fsetpos and ftell/fseek? What are fgetpos and fsetpos good for?
What is the difference between fgetpos/fsetpos and ftell/fseek? What are fgetpos and fsetpos good for? ftell and fseek use type long int to represent offsets (positions) in a file, and may therefore be limited to offsets which can be represented in a long int. (Type long int is not guaranteed to hol... 2015-10-14, 2705👍, 0💬

I im trying to declare a pointer and allocate some space for it
I'm trying to declare a pointer and allocate some space for it, but it's not working. What's wrong with this code? char *p; *p = malloc(10); The pointer you declared is p, not *p. When you're manipulating the pointer itself (for example when you're setting it to make it point somewhere), you just us... 2016-06-10, 2678👍, 0💬

How can I dynamically allocate arrays?
How can I dynamically allocate arrays? The equivalence between arrays and pointers allows a pointer to malloc'ed memory to simulate an array quite effectively. After executing #include &lt;stdlib.h> int *dynarray; dynarray = malloc(10 * sizeof(int)); (and if the call to malloc succeeds), you can... 2016-04-23, 2631👍, 0💬

I have heard that some operating systems dont actually allocate...
I've heard that some operating systems don't actually allocate malloc'ed memory until the program tries to use it. Is this legal? It's hard to say. The Standard doesn't say that systems can act this way, but it doesn't explicitly say that they can't, either. (Such a ``deferred failure'' implementati... 2016-04-21, 2605👍, 0💬

How can I find out how much memory is available?
How can I find out how much memory is available? Your operating system may provide a routine which returns this information, but it's quite system-dependent. (Also, the number may vary over time.) If you're trying to predict whether you'll be able to allocate a certain amount of memory, just try it-... 2016-04-23, 2583👍, 0💬

I wrote a little wrapper around malloc ...
I wrote a little wrapper around malloc, but it doesn't work: #include lt;stdio.h> #include lt;stdlib.h> mymalloc(void *retp, size_t size) { retp = malloc(size); if(retp == NULL) { fprintf(stderr, "out of memory\n"); exit(EXIT_FAILURE); } } Are you sure the function initialized what you thought it di... 2016-06-10, 2559👍, 0💬

How can I print numbers with commas separating the thousands? What about currency formatted numbers?
How can I print numbers with commas separating the thousands? What about currency formatted numbers? The functions in &lt;locale.h> begin to provide some support for these operations, but there is no standard C function for doing either task. (In Standard C, the only thing printf does in respons... 2015-11-02, 2504👍, 0💬

What does it mean?
Is char a[3] = "abc"; legal? What does it mean? It is legal in ANSI C (and perhaps in a few pre-ANSI systems), though useful only in rare circumstances. It declares an array of size three, initialized with the three characters 'a', 'b', and 'c', without the usual terminating '\0' character. The arra... 2015-12-09, 2445👍, 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