C Interview Questions And Answers

C Objective Interview Questions And Answers(10)

C Subjective Interview Questions And Answers(100)     

C syntax, semantics and simple programming questions(61)    

C Aptitude Questions(179) Objectives 

C Aptitude Questions

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C Aptitude Questions   

Questions 151
 #include <stdio.h>
main()
{
char * str = "hello";
char * ptr = str;
char least = 127;
while (*ptr++)
                  least = (*ptr<least ) ?*ptr :least;
printf("%d",least);
}

Answer:
0

Explanation:
After ‘ptr’ reaches the end of the string the value pointed by ‘str’ is ‘\0’. So the value of ‘str’ is less than that of ‘least’. So the value of ‘least’ finally is 0. 

Questions 152
Declare an array of N pointers to functions returning pointers to functions returning pointers to characters?

Answer:
            (char*(*)( )) (*ptr[N])( ); 

Questions 153
  main()
   {
struct student
{
char name[30];
struct date dob;
}stud;
struct date
        {  
         int day,month,year;
         };

     scanf("%s%d%d%d", stud.rollno, &student.dob.day, &student.dob.month,      &student.dob.year);
}

Answer: Compiler Error: Undefined structure date

Explanation:
Inside the struct definition of ‘student’ the member of type struct date is given. The compiler doesn’t have the definition of date structure (forward  reference is not allowed in C in this case) so it issues an error.

Questions 154
  main()
  {
struct date;
struct student
{
char name[30];
struct date dob;
}stud;
struct date
            {
         int day,month,year;
 };
scanf("%s%d%d%d", stud.rollno, &student.dob.day, &student.dob.month, &student.dob.year);
}
Answer:
Compiler Error: Undefined structure date

Explanation:
Only declaration of struct date is available inside the structure definition of ‘student’ but to have a variable of type struct date the definition of the structure is required.

Questions 155
There were 10 records stored in “somefile.dat” but the following program printed 11 names. What went wrong?
void main()
{
struct student
{    
char name[30], rollno[6];
}stud;
FILE *fp = fopen(“somefile.dat”,”r”);
while(!feof(fp))
 {
            fread(&stud, sizeof(stud), 1 , fp);
puts(stud.name);
}
}

Explanation:
fread reads 10 records and prints the names successfully. It will return EOF only when fread tries to read another record and fails reading EOF (and returning EOF). So it prints the last record again. After this only the condition feof(fp) becomes false, hence comes out of the while loop.

Questions 156
Is there any difference between the two declarations,
1.    int foo(int *arr[]) and
2.    int foo(int *arr[2])

Answer:

No

Explanation:
Functions can only pass pointers and not arrays. The numbers that are allowed inside the [] is just for more readability. So there is no difference between the two declarations.

Questions 157
What is the subtle error in the following code segment?

void fun(int n, int arr[])
{
int *p=0;
int i=0;
while(i++<n)
            p = &arr[i];
*p = 0;
}

Answer & Explanation:
If the body of the loop never executes p is assigned no address. So p remains NULL where *p =0 may result in problem (may rise to runtime error “NULL pointer assignment” and terminate the program).    

Questions 158
What is wrong with the following code? 

int *foo()
{
int *s = malloc(sizeof(int)100);
assert(s != NULL);
return s;
}

Answer & Explanation:
assert macro should be used for debugging and finding out bugs. The check s != NULL is for error/exception handling and for that assert shouldn’t be used. A plain if and the corresponding remedy statement has to be given.

Questions 159
 What is the hidden bug with the following  statement?

assert(val++ != 0);

Answer & Explanation:
Assert macro is used for debugging and removed in release version. In assert, the experssion involves side-effects. So the behavior of the code becomes different in case of debug version and the release version thus leading to a subtle bug.

Rule to Remember:

Don’t use expressions that have side-effects in assert statements. 

Questions 160
  void main()
{
int *i = 0x400;  // i points to the address 400
*i = 0;           // set the value of memory location pointed by i;
}
Answer:
Undefined behavior

Explanation:
The second statement results in undefined behavior because it points to some location whose value may not be available for modification.  This type of pointer in which the non-availability of the implementation of the referenced location is known as 'incomplete type'.

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