C Interview Questions - Set 2

C Programming Interview Questions

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This page consists of C Programming interview questions and answers.

Q1: Print "Hello World" without using semicolon in C programming language

For this we can write the following code.

#include <stdio.h>

int main() {
  if ( printf("Hello World") ) { }
  return 0;
}

Or we can write the following.

#include <stdio.h>

int main() {
  if ( printf("Hello World") );
  return 0;
}

Note! The printf() function will return the total number of characters printed and we can use this inside the if-statement to print the message "Hello World" without using a semicolon.

Q2: What is a NULL pointer?

If a pointer is assigned the NULL value then it becomes a NULL pointer. A NULL pointer points nowhere.

Following is an example of a NULL pointer.

int *ptr = NULL;

Q3: What is a dangling pointer?

Any pointer that does not points at a valid memory address is called a dangling pointer.

Q4: Create a dangling pointer in C programming language

In the following code we are creating a dangling pointer.

#include <stdio.h>
#include <stdlib.h>

int main() {
  
  // integer variable i
  int i = 10;

  // allocate memory to integer
  // pointer
  int *ptr = (int *) malloc (1 * sizeof(int));

  // assign address of integer
  // variable to integer pointer
  // variable
  ptr = &i;

  // this is now a dangling pointer
  free(ptr);

  // this will not work
  printf("value of i = %d\n", *ptr);

  return 0;
}

Q5: What is the difference between malloc() and calloc() in C programming?

Both are used to allocate memory space but calloc() by default fills the allocated memory space with 0.

Click here to learn more about malloc and calloc.

Q6: What do you understand by the term base address of an array?

The base address means the starting address of an array.

Q7: Write the output of the following C code

C code:

int arr[] = {10, 20, 30, 40, 50};
int c = 5;
int i = 0;
while (i < c) {
  printf("%d\n", arr[i % 2 == 0 ? i : i - 1]);
  i++;
}

Answer:

The above code will print the following.

10
10
30
30
50

In the above code we are using the ternary operator. If i is even the code is printing the value pointed by i in the array arr.

If i is odd the code is printing the value pointer by (i - 1) in the array arr.

Q8: Define constant

A variable whose value will not change is called a constant.

We can write the following code to create a constant in C programming language.

const int num = 100;

Q9: Which built-in function will you use to match a pattern in a given string?

To match a pattern in a given string we can use the strstr function.

Q10: Write C code to check if a pattern "lo" is present in the string "Hello World"

We can write the following C code to check the pattern.

#include <stdio.h>
#include <string.h>

int main() {
  char *str = "Hello World";
  char *ptrn = "lo";

  if (strstr(str, ptrn)) {
    printf("Pattern '%s' is present in string '%s'.\n", ptrn, str);
  } else {
    printf("Pattern not found.\n");
  }

  return 0;
}
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