1. What does static variable mean?
Ans: Static variables are the variables which retain their values between the function calls. They are initialized only once their scope is within the function in which they are defined.
2. What is a pointer?
Ans: Pointers are variables which stores the address of another variable. That variable may be a scalar (including another pointer), or an aggregate (array or structure). The pointed-to object may be part of a larger object, such as a field of a structure or an element in an array.
Ans: Static variables are the variables which retain their values between the function calls. They are initialized only once their scope is within the function in which they are defined.
2. What is a pointer?
Ans: Pointers are variables which stores the address of another variable. That variable may be a scalar (including another pointer), or an aggregate (array or structure). The pointed-to object may be part of a larger object, such as a field of a structure or an element in an array.
3. What are the uses of a pointer?
Ans: Pointer is used in the following cases
i) It is used to access array elements
ii) It is used for dynamic memory allocation.
iii) It is used in Call by reference
iv) It is used in data structures like trees, graph, linked list etc.
Ans: Pointer is used in the following cases
i) It is used to access array elements
ii) It is used for dynamic memory allocation.
iii) It is used in Call by reference
iv) It is used in data structures like trees, graph, linked list etc.
4. What is a structure?
Ans: Structure constitutes a super data type which represents several different data types in a single unit. A structure can be initialized if it is static or global.
Ans: Structure constitutes a super data type which represents several different data types in a single unit. A structure can be initialized if it is static or global.
5. What is a union?
Ans: Union is a collection of heterogeneous data type but it uses efficient memory utilization technique by allocating enough memory to hold the largest member. Here a single area of memory contains values of different types at different time. A union can never be initialized.
Ans: Union is a collection of heterogeneous data type but it uses efficient memory utilization technique by allocating enough memory to hold the largest member. Here a single area of memory contains values of different types at different time. A union can never be initialized.
6. What are the differences between
structures and union?
Ans: A structure variable contains each of the named members, and its size is large enough to hold all the members. Structure elements are of same size.
A union contains one of the named members at a given time and is large enough to hold the largest member. Union element can be of different sizes.
Ans: A structure variable contains each of the named members, and its size is large enough to hold all the members. Structure elements are of same size.
A union contains one of the named members at a given time and is large enough to hold the largest member. Union element can be of different sizes.
7. What are the differences between
structures and arrays?
Ans: Structure is a collection of heterogeneous data type but array is a collection of homogeneous data types.
Array
1-It is a collection of data items of same data type.
2-It has declaration only
3-.There is no keyword.
4- array name represent the address of the starting element.
Structure
1-It is a collection of data items of different data type.
2- It has declaration and definition
3- keyword struct is used
4-Structure name is known as tag it is the short hand notation of the declaration.
Ans: Structure is a collection of heterogeneous data type but array is a collection of homogeneous data types.
Array
1-It is a collection of data items of same data type.
2-It has declaration only
3-.There is no keyword.
4- array name represent the address of the starting element.
Structure
1-It is a collection of data items of different data type.
2- It has declaration and definition
3- keyword struct is used
4-Structure name is known as tag it is the short hand notation of the declaration.
8. In header files whether functions
are declared or defined?
Ans: Functions are declared within header file. That is function prototypes exist in a header file,not function bodies. They are defined in library (lib).
Ans: Functions are declared within header file. That is function prototypes exist in a header file,not function bodies. They are defined in library (lib).
9. What are the differences between
malloc () and calloc ()?
Ans: Malloc Calloc 1-Malloc takes one argument Malloc(a);where a number of bytes 2-memory allocated contains garbage values
1-Calloc takes two arguments Calloc(b,c) where b no of object and c size of object
2-It initializes the contains of block of memory to zerosMalloc takes one argument, memory allocated contains garbage values.
It allocates contiguous memory locations. Calloc takes two arguments, memory allocated contains all zeros, and the memory allocated is not contiguous.
Ans: Malloc Calloc 1-Malloc takes one argument Malloc(a);where a number of bytes 2-memory allocated contains garbage values
1-Calloc takes two arguments Calloc(b,c) where b no of object and c size of object
2-It initializes the contains of block of memory to zerosMalloc takes one argument, memory allocated contains garbage values.
It allocates contiguous memory locations. Calloc takes two arguments, memory allocated contains all zeros, and the memory allocated is not contiguous.
10. What are macros? What are its
advantages and disadvantages?
Ans: Macros are abbreviations for lengthy and frequently used statements. When a macro is called the entire code is substituted by a single line though the macro definition is of several lines.
The advantage of macro is that it reduces the time taken for control transfer as in case of
function.
The disadvantage of it is here the entire code is substituted so the program becomes
lengthy if a macro is called several times.
Ans: Macros are abbreviations for lengthy and frequently used statements. When a macro is called the entire code is substituted by a single line though the macro definition is of several lines.
The advantage of macro is that it reduces the time taken for control transfer as in case of
function.
The disadvantage of it is here the entire code is substituted so the program becomes
lengthy if a macro is called several times.
11. Difference between pass by reference and pass by value?
Ans: Pass by reference passes a pointer to the value. This allows the callee to modify the variable directly.Pass by value gives a copy of the value to the callee. This allows the callee to modify the value without modifying the variable. (In other words, the callee simply cannot modify the variable, since it lacks a reference to it.)
12. What is static identifier?
Ans: A file-scope variable that is declared static is visible only to functions within that file. A
function-scope or block-scope variable that is declared as static is visible only within that scope. Furthermore, static variables only have a single instance. In the case of function- or block-scope variables, this means that the variable is not “automatic” and thus retains its value across function invocations.
13. Where is the auto variables stored?
Ans: Auto variables can be stored anywhere, so long as recursion works. Practically, they’re stored on the stack. It is not necessary that always a stack exist. You could theoretically allocate function invocation records from the heap.
14. Where does global, static, and local, register variables, free memory and C Program instructions get stored?
Ans: Global: Wherever the linker puts them. Typically the “BSS segment” on many platforms.
Static: Again, wherever the linker puts them. Often, they’re intermixed with the globals. The only difference between globals and statics is whether the linker will resolve the symbols across compilation units.Local: Typically on the stack, unless the variable gets register allocated and never spills.Register: Nowadays, these are equivalent to “Local” variables. They live on the stack unless they get register-allocated.
15. Difference between arrays and linked list?
Ans: An array is a repeated pattern of variables in contiguous storage. A linked list is a set of
structures scattered through memory, held together by pointers in each element that point to the next element. With an array, we can (on most architectures) move from one element to the next by adding a fixed constant to the integer value of the pointer. With a linked list, there is a “next” pointer in each structure which says what element comes next.
16. What are enumerations?
Ans: They are a list of named integer-valued constants. Example:enum color { black , orange=4,
yellow, green, blue, violet };This declaration defines the symbols “black”, “orange”, “yellow”, etc. to have the values “1,” “4,” “5,” … etc. The difference between an enumeration and a macro is that the enum actually declares a type, and therefore can be type checked.
17. Describe about storage allocation and scope of global, extern, static, local and register variables?
Ans: Globals have application-scope. They’re available in any compilation unit that includes an
appropriate declaration (usually brought from a header file). They’re stored wherever the linker puts them, usually a place called the “BSS segment.”
Extern? This is essentially “global.”
Static: Stored the same place as globals, typically, but only available to the compilation unit that contains them. If they are block-scope global, only available within that block and its subblocks.
Local: Stored on the stack, typically. Only available in that block and its subblocks.
(Although pointers to locals can be passed to functions invoked from within a scope where that local is valid.)
Register: See tirade above on “local” vs. “register.” The only difference is that
the C compiler will not let you take the address of something you’ve declared as “register.”
18. What are register variables? What are the advantages of using register variables?
Ans: If a variable is declared with a register storage class,it is known as register variable.The
register variable is stored in the cpu register instead of main memory.Frequently used variables
are declared as register variable as it’s access time is faster.
19. What is the use of typedef?
Ans: The typedef help in easier modification when the programs are ported to another machine.
A descriptive new name given to the existing data type may be easier to understand the code.
20. Can we specify variable field width in a scanf() format string? If possible how?
Ans: All field widths are variable with scanf(). You can specify a maximum field width for a given
field by placing an integer value between the ‘%’ and the field type specifier. (e.g. %64s). Such a specifier will still accept a narrower field width.
The one exception is %#c (where # is an integer). This reads EXACTLY # characters, and it is the
only way to specify a fixed field width with scanf().