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74) Is using exit() the same as using return?

No. The exit() function is used to exit your program and return control to the operating system. The return statement is used to return from a function and return control to the calling function. If you issue a return from the main() function, you are essentially returning control to the calling function, which is the operating system. In this case, the return statement and exit() function are similar. 

75) Is it valid to address one element beyond the end of an array?

It's valid to address it, but not to see what's there. (The really short answer is, "Yes, so don't worry about it.") With most compilers, if you say 

int i, a[MAX], j;

Then either i or j is at the part of memory just after the last element of the array. The way to see whether i or j follows the array is to compare their addresses with that of the element following the array. The way to say this in C is that either 

& i == & a[ MAX ]

is true or

& a[ MAX ] == & j

is true. This isn't guaranteed.

1) What is the difference between #include and #include "file" ?

We use # include to include a file. The difference between two ways of file inclusion lies in the order in which preprocessor searches for the file specified. When the preprocessor encounters #include statement, it looks for the file specified in the angled brackets in the default location (Path defined in INCLUDE environment variable of the system). 

When # include followed by file name in double quotation marks is encountered by the preprocessor, it looks for the file in the current directory. If the file is not found in the current directory, it will look for the file in the default location. 

2) Can #include handle other file formats than .h?

Yes. Irrespective of the file type, Preprocessor will do its job and will include any file like test.z.

3) What is a void pointer?

A void pointer is a special pointer type which can point to any data type without letting the compiler know. It helps to pass a pointer to some function of any type which can be decided at run time. In the following example input parameter a and b can be both integer and string. 

Void PointerVoid(int type, void *a, void *b, void *c)


if(type == 1)/* int*/

*c = ((int) *a) + ((int)*b);

else /*string*/



4) What is the value of NULL?

The value of NULL is 0 or (void*)0. Whenever NULL has to be compared with some variable or assigned to a variable, depending upon the type of that variable, the value of NULL will be decided. 

5) Can the size of an array be declared at runtime?

No. The size of an array must be stated at the time of compilation. Alternate way is to use dynamic allocation by calloc or malloc.

7) What is the heap in memory?

The heap is where malloc(), calloc(), and realloc() get memory. The allocation of memory from the heap is much slower than the stack. But, the heap is much more flexible about memory allocation than the stack. Memory can be allocated and deallocated in any time and order. This heap memory isn't deallocated by itself, method free() has to be called in order to do so. 

8) What will be the output of the following code snippet?

float num1 = 6 / 4;

float num2 = 6 / 4.0;

printf("6/4 == %f or %f\n", num1, num2);

Output will be : 6/4 == 1.000000 or 1. 500000. This is a case of operator promotion. The variable num1 is set to “6/4”. Because, both 3 and 4 are integers. So integer division is performed on them and the result is the integer 0. The variable num2 is set to “6/4.0”. Because 4.0 is a float, the number 6 is converted to a float as well, and the result will be floating value 1.5. 

9) What happens if you free a pointer twice?

It is really dangerous to free the same memory twice. If the memory has not been reallocated in between, it will generate a “double free” error, since the memory location has already been freed. 

10) How does free() method know about how much memory to release?

There's no concrete way. Most systems, keeps a track of each memory block as linked lists. When memory is allocated, all the blocks that are given to that particular call are put into a linked list and the size, block number and serial number are written in the head node. There is no assurance, though. But in some way or other, the system keeps track of each block to know the size of each allocated portion of the heap. 

11) How to restrict a header file from including more than once?

In C, to avoid double inclusion, we use a include guard also known as macro guard. It is #ifndef - #endif pair. "ifndef" is an indication of “if not defined”. 

#ifndef FAMILY_H

#define FAMILY_H

struct Example


int member;


#endif /* FAMILY _H */

12) How to print an address?

The best way is to use "%p" in printf() or fprintf. The “%p” will tell compiler to use the best type to use, while printing the address according to the environment, since the size of a pointer changes from system to system. 

13) Enter the output of the program

#include stdio.h

enum day {sunday = 1,monday,tuesday,wednesday,thursday = 3,friday,saturday};

int main()


int i;

printf("%d %d %d %d %d %d %d", sunday, monday, tuesday,

wednesday, thursday, friday, saturday);


return 0;


The answer is : 1 2 3 4 3 4 5

Explanation: The enum assigns the value with single increment. If a value is explicitly assigned to an element, it will just set that value to that element and start to increment from that assigned value for the following elements. 

14) Explain recursive functions? Also explain the advantages and disadvantages of Recursive algorithms? 

A recursive function is a function which calls itself. The advantages of recursive functions are:

• A substitute for very complex iteration. For example, a recursive function is best to reduce the code size for Tower of Hanoi application. 

• Unnecessary calling of functions can be avoided.

The disadvantages of Recursive functions:

• The exit point must be explicitly coded ,otherwise stack overflow may happen

• A recursive function is often confusing. It is difficult to trace the logic of the function. Hence, it is difficult to debug a recursive function. 

15) What are the standard predefined macros?

ANSI C has six predefined macro. They are

• __FILE__ - Name of the current file

• __LINE__ - Current line number

• __TIME__ - Current time of compilation

• __DATE__ - Current date of compilation

• __cplusplus - If program compiled in C++ compiler

• __STDC__ - If ANSI C is followed by the compiler strictly.

16) What is a pragma?

The #pragma preprocessor allows compiler to include or exclude compiler specific features. For example if there is a feature xxx_yyy then, 

#pragma xxx_yyy(on)

Forces compiler to include the feature. Conversely, you can turn off it by the following lines:

#pragma xxx_yyy(off)

17) How to redefined macro with different value?

The #undef preprocessor can be used to reset a macro. For example,

#ifdef SAMPLE /* Checking if SAMPLE is defined */

#undef SAMPLE /* If so, then reset it */


#define SAMPLE 0 /* Then redefine with intended value */

18) What is an lvalue?

An lvalue is an expression to which a value can be assigned. The lvalue expression is the one which is located on the left side a statement, whereas an rvalue is located on the right side of a statement. Each assignment must have a valid lvalue and rvalue. The lvalue expression must refer to a storage where something can be stored. It can't be a constant. 

19) How to assign one array to another?

You can't assign an array to other. Arrays are not lvalue, because they don't refer to one variable, rather a set of variables. So they can't be placed on the left hand side of an assignment statement. For example the following statement will generate compilation error. 

int x[5], y[5];

x = y;

20) what is the order of operator precedence, left to right or right to left ?

None of them is standard. C does not always start evaluating left to right or right to left. Normally, function calls are done first, followed by complex expressions and then simple expressions. That is why it is best to use parenthesis in all expressions, without depending on precedence. 

21) What is the difference between ++X and X++?

The ++ operator is called the incremental operator. When the operator is placed before, the variable is incremented by 1 before it is used in the statement. When the operator is placed after the variable, then the expression is evaluated first and then the variable is incremented by 1. 

22) What happens when we use incremental operator in a pointer?

It depends upon the type of the pointer. It gets incremented by the size of the data type, the pointer is pointing to. For example

char p; p++; /* here p increments by 1*/

int p; p++;/* here p increments by 4(for 32 bit system)*/

23) What will be output of the following code snippet?

int num1=5;

int num2=5;

num1 =num1++ + num1--;

num2 =++num2 + --num2;

printf("num1=%d num2=%d",num1,num2);

Output will be num1=10 num2=10.

24) Can the sizeof operator be used to tell the size of an array passed to a function?

No. The sizeof() operator can't tell the size of an array, because it is actually a pointer to the data type of the array.

25) Can you change the value of an array tag?

No. An array tag can't be used as a storage, because it is not an Lvalue. It can be thought as a pointer to the datatype of the array which is constant and which can't be changed or assigned dynamically. 

27) What are text and binary modes?

Streams can be classified into two types: text streams and binary streams. The text streams are interpreted as per the ASCII values starting from 0 to 255. Binary streams are raw bytes which C can't interpret, but application has to interpret it itself. Text modes are used to handle, generally text file where as binary modes can be used for all files. But they won't give you the content of a file, rather they will give you the file properties and content in raw binary format. 

28) Which one to use, a stream function or a system calls?

Stream files are generally better to use, since they provide sufficient amount of buffer for read and write. That is why it is more efficient. But in a multiuser environment, files can be shared among users. These shared files are secured with lock, where only one user will be able to write at a time. In this scenario, buffering will not be efficient, since the file content will change continuously and it will be slower. So, normally it is good to use stream functions, but for shared files system calls are better. 

29) What is the difference between a string copy (strcpy) and a memory copy (memcpy)?

Generally speaking, they both copy a number of bytes from a source pointer to a destination pointer. But the basic difference is that the strcpy() is specifically designed to copy strings, hence it stops copying after getting the first '\0'(NULL) character. But memcpy() is designed to work with all data types. So you need to specify the length of the data to be copied, starting from the source pointer. 

30) How can I pad a string to a known length?

printf("%-20.20s", data[d]);

The "%-20.20s" argument tells the printf() function that you are printing a string and you want to force it to be 20 characters long. By default, the string is right justified, but by including the minus sign (-) before the first 20, you tell the printf() function to left-justify your string. This action forces the printf() function to pad the string with spaces to make it 20 characters long. 

34) When should a type cast be used?

There are two main uses of type cast.

• The first one is to convert some value of datatype A to a datatype B. Such as, if you type cast a float variable of value 1.25 to int, then it will be 1. • The second use is to cast any pointer type to and from void *, in order to use it in generic functions such as memory copy functions, where the execution is independent of the type of the pointer. 

35) What is the difference between declaring a variable and defining a variable?

Declaration is done to tell compiler the data type of the variable, and it inherently meant that somewhere in this scope, this variable is defined or will be defined. And defining a variable means to allocate space for that variable and register it in the stack memory. For example: extern int decl1; /* this is a declaration */

int def2; /* this is a definition */ 

36) Can static variables be declared in a header file?

You can't declare a static variable without definition (this is because they are mutually exclusive storage classes). A static variable can be defined in a header file, but then every source file with in that scope will have their own copy of this variable, which is intended. 

37) What is the benefit of using const for declaring constants over #define?

The basic difference between them is that, a const variable is a real variable which has a datatype and it exists at run time, and it can't be altered. But a macro is not a real variable, but it carries a constant value which replaces all the occurrences of that macro at the time of pre-processing. 

38) What is a static function?

Static function is a special type of function whose scope is limited to the source file where the function is defined and can not be used other than that file. This feature helps you to hide some functions and to provide some standard interface or wrapper over that local function. 

39) Should a function contain a return statement if it does not return a value?

In C, void functions does not return anything. So it is useless to put a return statement at the end of the function, where the control will any way return to the caller function. But, if you want to omit some portion of the function depending upon the scenario, then this return statement is perfect to avoid further execution of that void function. 

40) How can you pass an array to a function by value?

An array can be passed to a function by value, by keeping a parameter with an array tag with empty square brackets(like []). From the caller function, just pass the array tag. For instance, 

void func(int i[]) {..} /* parameter */


int k[10];

func(k); /* caller function */

41) Is it possible to execute code even after the program exits the main() function?

There is a standard C function named atexit() for this purpose that can be used to perform some operations when your program exiting. You can register some functions with atexit() to be executed at the time of termination. Here's an example: 

#include stdio.h

#include stdlib.h

void _some_FUNC_(void);

int main(int argc, char** argv)






42) What does a function declared as PASCAL do differently?

In C, when some function is called, the parameters are put at the top of the stack. Now the order in which they are put is the order in which the parameters are parsed. Normally, the order is right to left. That is, the right most is parsed first and the left most parameter is parsed at last. 

If you want to alter this paradigm, then you have to define the function with PASCAL as following:

int PASCAL pascal_func(int, char*, long);

Here, the left most parameter(int) will be parsed first, then char* and then long.

43) Why does PASCAL matter? Is there any benefit to using PASCAL functions?

The main reason behind using PASCAL is that, in the left-to-right parsing the efficiency of switching increases in C.

44) Is using exit() the same as using return?

No. They are not the same. Return statement returns control to the caller function, that is, it exits from the lowest level of the call stack. Where as, exit statement make the program returns to the system from where the application was started. So, exit always exits from the highest level of call stack. Eventually, if there is only one level of function call then they both do the same.

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Disclaimer: All the above contents are provided by Google Group members. 
Further, this content is not intended to be used for commercial purpose. is not liable/responsible for any copyright issues.

Copyright Disclaimer:Section 107 of the Copyright Act Fair Use Contents .
We are forwarding content link(s) from our website to content website & We are not serving any contents. Main the Content PDF link(s) is/are obtained from GoogleSearch for the purpose of Education & Teaching Intention. Not for commercial purpose. is not liable/responsible for any copyright issues.

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