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.
A pointer is declared as:
int *ap;
int a = 5;
In the above two statements an integer a was declared and
initialized to 5. A pointer to an integer with name ap was declared.
Next before ap is used
ap=&a;
This operation would initialize the declared pointer to int.
The pointer ap is now said to point to a.
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.
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.
int roll_number;
char name[30];
int total_marks;
This concept would be particularly useful in grouping data
types. You could declare a structure student as:
struct student {
int roll_number;
char name[30];
int total_marks;
} student1, student2;
The above snippet of code would declare a structure by name
student and it initializes two objects student1, student2. Now these objects
and their fields could be accessed by saying student1.
roll_number for accessing roll number field of
student1 object, similarly student2.
name for accessing name field of student 2 object.
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.
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.
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.
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).
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.
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.
#include
#include
#define SQUARE(x) x*x
int main() {
int i = 2;
int j= SQUARE(i);
printf("The
value of j is: %d\n", j);
getch();
return 0;
}
The following line defines the macro SUM as having two
parameters a and b and the replacement tokens (a + b):
#define SUM(a,b) (a + b)
This definition would cause the preprocessor to change the
following statements (if the statements appear after the previous definition):
c = SUM(x,y);
c = d * SUM(x,y);
In the output of the preprocessor, these statements would
appear as:
c = (x + y);
c = d * (x + y);
Use parentheses to ensure correct evaluation of replacement
text. For example, the definition:
#define SQR(c) ((c) *
(c))
requires parentheses around each parameter c in the
definition in order to correctly evaluate an expression like:
y = SQR(a + b);
The preprocessor expands this statement to:
y = ((a + b) * (a + b));
Without parentheses in the definition, the correct order of
evaluation is not preserved, and the preprocessor output is:
y = (a + b * a + b);
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.)
Pass By Reference :
In Pass by reference address of the variable is passed to a
function. Whatever changes made to the formal parameter will affect to the
actual parameters
- Same memory location is used for both variables.(Formal
and Actual)-
- it is useful when you required to return more then 1
values
Pass By Value:
- In this method value of the variable is passed. Changes
made to formal will not affect the actual parameters.
- Different memory locations will be created for both
variables.
. where as
in pass by reference the change in the variable may reflect
to the original value in the main funtion.
ex : // Pass by
Reference
void Get( int &nIndex){
nIndex = 10;
}
void main()
{
int x = 100;
cout<
}
o/p : 10;
in Pass by value; if any change in variable in the sub-
function may not reflected to the main function
ex : // Pass by Value
void Get( int nIndex){
nIndex = 10;
}
void main()
{
int x = 999;
cout<
}
o/p : 999
