Technical Interview

C Interview Questions

Several jobs require candidates to have a profound knowledge of C. These C Interview Questions have been designed specially to get you acquainted with the nature of questions that you may encounter during your interview for the subject of C.

1. What is C language?

C is a procedural and general-purpose programming language created by Dennis Ritchie in 1972 at the Bell Telephone Laboratories. It was invented to write UNIX operating system. C is the most widely used computer language. The main features of C language include low-level access to memory, easy to learn and modular structure which makes code debugging, maintenance, and testing easier. Due to these features make C language suitable for system programmings like an operating system or compiler development.

2. What are the features of C Programming Language?

Some important features of C programming language are given below:

  • Simple Language - C is a simple language. It is very easy to understand and learn.
  • Mid-Level Language – C is a mid-level language and enables low-level language featuress like development of system applications such as kernel and drivers. It also supports the feature of high-level language. Hence C is a mid-level language.
  • Machine Independent Language – C can be interpreted on various operating systems including UNIX-based systems, Linux, Mac OS and various versions of Windows.
  • Case-Sensitive Language - C is a case sensitive language and treats the uppercase and lowercase characters in a different manner.
  • Structured Programming Language – C is a structured programming language that means any C program can be achieved in parts using functions. This makes any C program easy to understand and modify.
  • Rich Library Support – C provides lots of inbuilt functions which makes programming faster and easier. These functions can be accessed by including appropriate header file in the C program.
  • Powerful & Fast Language - C is a fast language as it takes very less time in compilation and execution.
  • Dynamic Memory Allocation - C supports the use of pointers which means a user can directly interact with memory and allocate memory dynamically.

3. What is a pointer in C?

A pointer is a variable which stores address of another variable.The address of a variable can be obtained by using ampersand sign (&), known as address-of operator followed by the name of a variable.

The value of a variable can also be accessed by using pointer. The * operator, known as dereference operator followed by the name of the pointer gives the value stored in the address pointed by the pointer.

//p1 is a pointer which stores address of variable
p1 = &Var;

//*p1 gives value of variable
x = *p1;

In the example below, an integer variable called MyVar and a pointer called p1 are created. pointer p1 is assigned the address of MyVar. Then, *p1 is used to get the value of MyVar as shown in the output.

#include <stdio.h>

int main (){
    int MyVar = 10;
    int *p1;
    p1 = &MyVar;
    return 0;

The output of the above code will be:



4. Write a program to swap two numbers without using the third variable.

This are many ways to swap two numbers. The example below uses + operator to swap two numbers.

#include <stdio.h>

static void swap(int, int);

static void swap(int x, int y) {
    printf("Before Swap.\n");
    printf("x = %i\n", x);
    printf("y = %i\n", y);

    //Swap technique
    x = x + y;
    y = x - y;
    x = x - y;

    printf("After Swap.\n");
    printf("x = %i\n", x);
    printf("y = %i\n", y);

int main() {
  swap(10, 25);

The output of the above code will be:

Before Swap.
x = 10
y = 25
After Swap.
x = 25
y = 10

5. Write a program to print Fibonacci series.

This are many ways to print the Fibonacci series in C. The example below uses dynamic programming to print the given term of Fibonacci series.

#include <stdio.h>

static int fib(int);

static int fib(int n) {
  //creating array which contains Fibonacci terms
  int f[n+1];
  f[0] = 0;
  f[1] = 1;
  for(int i = 2; i <= n ; i++)
    f[i] = f[i-1] + f[i-2];
  return f[n];

int main() {
  printf("Fibonacci 6th term: %i\n",fib(6));
  printf("Fibonacci 7th term: %i\n",fib(7));
  printf("Fibonacci 8th term: %i\n",fib(8));

The output of the above code will be:

Fibonacci 6th term: 8
Fibonacci 7th term: 13
Fibonacci 8th term: 21