C interview questions and answers

1. Write a c program without using any semicolon which output will : Hello word.


Solution: 1
void main(){
    if(printf("Hello world")){
    }
}
Solution: 2
void main(){
    while(!printf("Hello world")){
    }
}
Solution: 3
void main(){
    switch(printf("Hello world")){
    }
}

2. Write a C program to Swap two variables without using third variable.

int main()
{
    int a=5,b=10;
//process one
    a=b+a;
    b=a-b;
    a=a-b;
    printf("a= %d  b=  %d",a,b);

//process two
    a=5;
    b=10;
    a=a+b-(b=a);
    printf("\na= %d  b=  %d",a,b);
//process three
    a=5;
    b=10;
    a=a^b;
    b=a^b;
    a=b^a;
    printf("\na= %d  b=  %d",a,b);
  
//process four
    a=5;
    b=10;
    a=b-~a-1;
    b=a+~b+1;
    a=a+~b+1;
    printf("\na= %d  b=  %d",a,b);
  
//process five
    a=5,
    b=10;
    a=b+a,b=a-b,a=a-b;
    printf("\na= %d  b=  %d",a,b);
    getch();

}

3. 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.

Initially:

Later: 

4. What is wild pointer in c ?

A pointer in c which has not been initialized is known as wild pointer.

Example:

(q)What will be output of following c program?

void main(){
int *ptr;
printf("%u\n",ptr);
printf("%d",*ptr);

}

Output: Any address
Garbage value

Here ptr is wild pointer because it has not been initialized.
There is difference between the NULL pointer and wild pointer. Null pointer points the base address of segmentwhile wild pointer doesn�t point any specific memory location.

5. What is the meaning of prototype of a function ?

Prototype of a function
Answer: Declaration of function is known as prototype of a function. Prototype of a function means
(1) What is return type of function?
(2) What parameters are we passing?
(3) For example prototype of printf function is:
int printf(const char *, �);
I.e. its return type is int data type, its first parameter constant character pointer and second parameter is ellipsis i.e. variable number of arguments.


6. What are merits and demerits of array in c?

(a) We can easily access each element of array.
(b) Not necessity to declare two many variables.
(c) Array elements are stored in continuous memory location.

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