C Programming Interview Question and Answer SET 5

81. main()

{
show();
}
void show()
{
printf("I'm the greatest");
}

Answer: Compier error: Type mismatch in redeclaration of show.

Explanation: When the compiler sees the function show it doesn't know anything about it. So the default return type (ie, int) is assumed. But when compiler sees the actual definition of show mismatch occurs since it is declared as void. Hence the error.

The solutions are as follows:
1. declare void show() in main() .
2. define show() before main().
3. declare extern void show() before the use of show().

82.  main( )
{
int a[2][3][2] = {{{2,4},{7,8},{3,4}},{{2,2},{2,3},{3,4}}};
printf(“%u %u %u %d \n”,a,*a,**a,***a);
printf(“%u %u %u %d \n”,a+1,*a+1,**a+1,***a+1);
}

Answer:

100, 100, 100, 2
114, 104, 102, 3

Explanation: The given array is a 3-D one. It can also be viewed as a 1-D array.

2

4

7

8

3

4

2

2

2

3

3

4

100 102 104 106 108 110   112  114  116  118  120   122

thus, for the first printf statement a, *a, **a give address of first element. since the indirection ***a gives the value. Hence, the first line of the output.

for the second printf a+1 increases in the third dimension thus points to value at 114, *a+1 increments in second dimension thus points to 104, **a +1 increments the first dimension thus points to 102 and ***a+1 first gets the value at first location and then increments it by 1. Hence, the output.

83.  main( )

{
int a[ ] = {10,20,30,40,50},j,*p;
for(j=0; j<5; j++)
{
printf(“%d” ,*a);
a++;
}
p = a;
for(j=0; j<5; j++)
{
printf(“%d ” ,*p);
p++;
}
}

Answer: Compiler error: lvalue required.

Explanation: Error is in line with statement a++. The operand must be an lvalue and may be of any of scalar type for the any operator, array name only when subscripted is an lvalue. Simply array name is a non modifiable lvalue.

84.  main( )
{
static int a[ ] = {0,1,2,3,4};
int *p[ ] = {a,a+1,a+2,a+3,a+4};
int **ptr = p;
ptr++;
printf(“\n %d %d %d”, ptr-p, *ptr-a, **ptr);
*ptr++;
printf(“\n %d %d %d”, ptr-p, *ptr-a, **ptr);
*++ptr;
printf(“\n %d %d %d”, ptr-p, *ptr-a, **ptr);
++*ptr;
printf(“\n %d %d %d”, ptr-p, *ptr-a, **ptr);
}

Answer:

111
222
333
344

Explanation:  Let us consider the array and the two pointers with some address

                                   a

0

1

2

3

4

100  102   104  106  108

                          p

100

102

104

106

108

1000  1002   1004 1006  1008

     ptr

1000

2000

After execution of the instruction ptr++ value in ptr becomes 1002, if scaling factor for integer is 2 bytes. Now ptr – p is value in ptr –starting location of array p, (1002 – 1000) / (scaling factor) = 1,

*ptr – a = value at address pointed by ptr – starting value of array a, 1002 has a value 102 so the value is (102 – 100)/(scaling factor) = 1, **ptr is the value stored in the location pointed by the pointer of ptr = value pointed by value pointed by 1002 = value pointed by 102 = 1. Hence the output of the firs printf is 1, 1, 1.

After execution of *ptr++ increments value of the value in ptr by scaling factor, so it becomes1004. Hence, the outputs for the second printf are ptr – p = 2, *ptr – a = 2, **ptr = 2.

After execution of *++ptr increments value of the value in ptr by scaling factor, so it becomes1004. Hence, the outputs for the third printf are ptr – p = 3, *ptr – a = 3, **ptr = 3.

After execution of ++*ptr value in ptr remains the same, the value pointed by the value is incremented by the scaling factor. So the value in array p at location 1006 changes from 106 10 108,. Hence, the outputs for the fourth printf are ptr – p = 1006 – 1000 = 3, *ptr – a = 108 – 100 = 4, **ptr = 4.

85. What is dangling pointer in c?
If any pointer is pointing the memory address of any variable but after some variable has deleted from that memory location while pointer is still pointing such memory location. Such pointer is known as dangling pointer and this problem is known as dangling pointer problem.

86. What are merits and demerits of array in c?
Merits:
(a) We can easily access each element of array.
(b) Not necessity to declare too many variables.
(c) Array elements are stored in continuous memory location.

Demerits:
(a) Wastage of memory space. We cannot change size of array at the run time.
(b) It can store only similar type of data

87. Where are the auto variables stored?

Auto variables are stored in main memory and their default value is a garbage value.

88. Why Preincrement operator is faster than Postincrement?

Evaluation of any expression is from left to right. Preincrement is faster because it doesn't need to save the current value for next instruction whereas Postincrement needs to saves current value to be incremented after execution of current instruction.

89. Difference between arrays and linked list?

Major differences between arrays and linked lists are: (i)  In array consecutive elements are stored in consecutive memory locations whereas in linked list it not so. (ii)  In array address of next element is consecutive and whereas in linked list it is specified in the address part of each node.(iii) Linked List makes better use of memory than arrays.(iv) Insertion or deletion of an element in array is difficult than insertion or deletion in linked list

90. What is the use of typedef?

(i)It increases the portability.
(ii) It simplify the complex declaration and improve readability of the program.

91. What are library Functions?

Library Functions are predefined functions and stored in .lib files.

92. What is a structure?

Structure is a collection of heterogeneous (i.e. related data items which can be of different types) held together to a single unit. The data items enclosed within a structure are called its members which may be of data type int, float, char, array etc.

93. What is a pointer?

Pointer is a variable that contains address of another variable in the memory. Pointers are quite useful in creation of linked data structures (such as linked lst, trees graphs), managing object allocated memory dynamically, optimize the program to execute faster and use less memory.

94. What are the techniques you use for debugging?

(i)Using compiler’s features
(ii)Read The Fine Module
(iii)printf( ) debugging
(iv)Code grinding
(v)Assertion

 95. What are macros? What are its advantages and disadvantages?

Macro is a Pre-processor.Major advantage of using the macro is to increase the speed of the execution of the program.
Major disadvantage of the macros are:
(i) No type checking is performed in macro. This may cause error.
(ii)  A macro call may cause unexpected results.

96. What is difference between Structure and Unions?

(i)    In structure every member has its own memory whereas in union its members share the same member space.
(ii)  In structure, it is possible to initialize all the members at the same time which is not possible in case of union.
(iii) A structure requires more space than union(for the same type of members).
(iv) In union different interpretations of the same memory space are possible which is not so in case of structures.

97. What are the advantages of using Unions?

(i) Efficient use of memory as it it does not demand memory space for its all members rather it require memory space for its largest member only.
(ii) Same memory space can be interpreted differently for different members of the union.

98. What is the difference between ordinary variable and pointer in C?

An ordinary variable is like a container it can hold any value and we can change the value of ordinary variable at a time throughout the program .A pointer is a variable that stores the address of another Variable.

99. What are segment and offset addresses?
When paging technique is performed, the page will breaks into segments and its sequence is said to be segments and its width can be said as offset. In short,segment is a physical address and offset is logical address.

100. When should a type cast be used?

There are two situations in which to use a type cast. The first use is to change the type of an operand to an arithmetic operation so that the operation will be performed properly.
The second case is to cast pointer types to and from void * in order to interface with functions that expect or return void pointers. For example, the following line type casts the return value of the call to malloc() to be a pointer to a foo structure.
struct foo *p = (struct foo *) malloc(sizeof(struct foo));