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What is a ternary operator in c

The ternary operator, also known as the conditional operator, is a unique operator in C and many other programming languages. It provides a concise way to express conditional statements in a single line of code.

The syntax of the ternary operator is:

condition ? expression1 : expression2

Here’s how it works:

  • The condition is evaluated first.
  • If the condition is true (non-zero), expression1 is evaluated and becomes the result of the entire expression.
  • If the condition is false (zero), expression2 is evaluated and becomes the result of the entire expression.
  • In other words, the ternary operator acts as a shorthand for an if-else statement, where condition is the condition to be checked, expression1 is the value returned if the condition is true, and expression2 is the value returned if the condition is false.
#include <stdio.h>

int main() {
    int a = 10, b = 11;
    int result;

    // Using the ternary operator to determine if a is greater than b
    result = (a > b) ? 1 : 0;

    // Using the result in an if statement
    if (result == 1) {
        printf("a is greater than b\n");
    } else {
        printf("a is not greater than b\n");

    return 0;

Converting 32-bit Hexadecimal Data to 8-bit Format in C

#include <stdio.h>
#include <stdint.h>

int main() {
    uint32_t hexValue = 0xAABBCCDD; // Example 32-bit hexadecimal data
    uint8_t byte[4]; // Array to store 8-bit format

    // Converting 32-bit hex value to 8-bit format
    byte[0] = (hexValue >> 24) & 0xFF; // Extracting most significant byte
    byte[1] = (hexValue >> 16) & 0xFF;
    byte[2] = (hexValue >> 8) & 0xFF;
    byte[3] = hexValue & 0xFF; // Extracting least significant byte

    // Displaying the result
    printf("Original 32-bit hex value: 0x%X\n", hexValue);
    printf("8-bit format:\n");
    for (int i = 0; i < 4; i++) {
        printf("Byte %d: 0x%X\n", i+1, byte[i]);

    return 0;


  • The given 32-bit hexadecimal data 0xAABBCCDD is converted into an array of 8-bit values.
  • Each byte (8 bits) of the 32-bit data is extracted using bitwise right shifts (>>) and bitwise AND (&) operations to mask out the desired byte.
  • The resulting 8-bit format is then displayed, showing each byte separately.

Can you demonstrate how to manipulate individual bits in C, including setting, toggling, and deleting/Clear them?

#include <stdio.h>
#include <stdint.h>

// Function to set a specific bit in a given number
uint32_t setBit(uint32_t num, int pos) {
    return num | (1 << pos);

// Function to toggle a specific bit in a given number
uint32_t toggleBit(uint32_t num, int pos) {
    return num ^ (1 << pos);

// Function to delete (clear) a specific bit in a given number
uint32_t clearBit(uint32_t num, int pos) {
    return num & ~(1 << pos);

int main() {
    uint32_t num = 0b10101010; // Example number
    int pos = 2; // Position of the bit to manipulate

    // Setting the bit at position 'pos'
    printf("Setting bit at position %d: 0x%X\n", pos, setBit(num, pos));

    // Toggling the bit at position 'pos'
    printf("Toggling bit at position %d: 0x%X\n", pos, toggleBit(num, pos));

    // Deleting (clearing) the bit at position 'pos'
    printf("Clearing bit at position %d: 0x%X\n", pos, clearBit(num, pos));

    return 0;

Could you explain what structure padding is and how it benefits C programming

#include <stdio.h>

// Structure without padding
struct WithoutPadding {
    char a;
    int b;
    char c;

// Structure with padding
struct WithPadding {
    char a;
    char pad1[3]; // Padding added to align 'b' to a 4-byte boundary
    int b;
    char c;

int main() {
    // Size of structures
    printf("Size of struct WithoutPadding: %lu bytes\n", sizeof(struct WithoutPadding));
    printf("Size of struct WithPadding: %lu bytes\n", sizeof(struct WithPadding));

    return 0;

Candidate Explanation

Certainly! Structure padding is the process of adding additional bytes to a structure to ensure that each member of the structure is properly aligned in memory. The compiler often adds these padding bytes to optimize memory access and ensure efficient data retrieval. In C programming, structure members are typically aligned based on their data types. For example, integers often need to be aligned on 4-byte boundaries for optimal memory access. By padding the structure, the compiler can ensure that accessing structure members is more efficient, which can lead to better performance and memory utilization in the program.

Can you explain what the volatile keyword in C is used for and provide an example of its usage?

Candidate: “Certainly! The volatile keyword is used to inform the compiler that a variable’s value may change unexpectedly, without any action being taken by the code. This could happen due to external factors such as hardware registers, concurrent execution by multiple threads, or signal handlers. When a variable is declared as volatile, the compiler is instructed not to optimize accesses to that variable, ensuring that reads and writes are performed as expected.

Interviewer: Could you provide an example scenario where the volatile keyword is necessary?

Candidate: “Sure! Consider a scenario where we have a variable sensor_value representing data read from a sensor connected to a microcontroller. The value of sensor_value can change at any time due to external sensor readings, and the compiler should not optimize accesses to it. Therefore, we declare sensor_value as volatile to ensure that the compiler does not optimize away reads or reorder writes to the variable. This ensures that our program correctly reacts to changes in sensor data, as shown in the code example below.

#include <stdio.h>

volatile int sensor_value; // Declaring sensor_value as volatile

// Function to read sensor value
void read_sensor() {
    // Read sensor value from hardware
    sensor_value = read_sensor_data();

// Main program loop
int main() {
    while (1) {
        // Perform some processing based on sensor value
    return 0;

In this example, sensor_value is declared as volatile because its value can change asynchronously due to external hardware events. The volatile keyword ensures that the compiler does not optimize accesses to sensor_value, allowing the program to correctly read and react to changes in sensor data.

Interviewer: Let’s dive deeper into the concept of volatile variables. You mentioned that declaring a variable as volatile informs the compiler that its value may change unexpectedly. Could you explain why this is important in certain scenarios?

Without volatile:

  • If sensor_value is declared without volatile, the compiler may optimize access to the variable assuming its value does not change unexpectedly.
  • In such cases, the compiler might optimize by caching the value of sensor_value in a register or reordering read and write operations.
  • This optimization can lead to incorrect behaviour if the value of sensor_value changes asynchronously due to external factors (e.g., hardware interrupts, signal handlers, or concurrent threads), as the cached value may become stale.

With volatile:

  • By declaring sensor_value as volatile int sensor_value; the compiler is informed that the value of sensor_value may change unexpectedly and should not be optimized.
  • The compiler generates code that directly accesses the memory location of sensor_value whenever its value is read or written, ensuring that the most up-to-date value is used.
  • This prevents potential issues caused by optimizations such as caching or reordering, ensuring that the program correctly reacts to changes in sensor_value.

Could you explain the difference between the auto and register storage classes in C?

Candidate: “Certainly! Both auto and register are storage class specifiers in C, but they serve different purposes.


  • The auto storage class is the default storage class for local variables declared within functions.
  • Variables declared as auto are stored in the stack memory.
  • When a variable is declared as auto, it means that its storage duration is limited to the block or function in which it is declared.
  • While using auto is optional since it’s the default behaviour, explicitly declaring variables as auto can improve code readability by making the intent explicit.


  • The register storage class is used to suggest to the compiler that a variable should be stored in a CPU register for faster access.
  • Variables declared as registers are also stored in the stack memory but are accessed more efficiently because they are stored in registers.
  • However, the register keyword is just a hint to the compiler, and the compiler may choose to ignore it if it deems storing the variable in a register unnecessary.
  • Additionally, the use of a register is optional, and the compiler is free to ignore it if it cannot allocate a register or if it determines that using a register would not lead to performance improvement.

In summary, while both auto and register are storage class specifiers in C, auto is used to declare local variables with default storage behaviour, whereas register is used to suggest to the compiler that a variable should be stored in a CPU register for faster access.

Interviewer: Thank you for the explanation. Can you provide an example scenario where using register might be beneficial?

Candidate: “Certainly! In performance-critical sections of code, such as inner loops, where frequent access to a variable is required, using a register to suggest storing that variable in a CPU register can lead to performance improvements by reducing memory access times.

Example 1: Using auto Storage Class:

#include <stdio.h>

void autoExample() {
    auto int x = 10; // Declaring 'x' as auto, which is the default behavior for local variables
    printf("Value of auto variable 'x': %d\n", x);

int main() {
    return 0;

Example 2: Using register Storage Class:

#include <stdio.h>

void registerExample() {
    register int y = 20; // Declaring 'y' as register to suggest storing it in a CPU register
    printf("Value of register variable 'y': %d\n", y);

int main() {
    return 0;

Interviewer: Can you explain how to store data in a specific memory location, such as a register?

Candidate: “Certainly! To store data in a particular memory location, like a register, we typically use pointers to access that memory directly. However, it’s important to note that the use of register variables in C is merely a suggestion to the compiler, and the compiler may or may not honor this suggestion. Let me provide you with an example code snippet to demonstrate how this can be done.

#include <stdio.h>

int main() {
    // Declare a pointer to an integer and initialize it with the memory address of the register
    volatile int *register_ptr = (volatile int *)0x12345678; // Replace 0x12345678 with the actual memory address

    // Store data in the register memory location
    *register_ptr = 42;

    // Read data from the register memory location
    int data = *register_ptr;

    // Print the data read from the register
    printf("Data stored in the register: %d\n", data);

    return 0;

Could you please explain the memory sizes of integer, character, integer pointer, and character pointer in C?

Data TypeSize (in bytes)
long long8
long double12 or 16

Write a program for Big-endian and little-endian

#include <stdio.h>

typedef union
    unsigned int n;
    char bytes[4];

int main()
    EndianCheck endianCheck;
    endianCheck.n = 0x11223344;
    printf(" %x\n",endianCheck.bytes[1]);
    if(endianCheck.bytes[0] == 11)
        printf(" BigIndian\n");
    else {
        printf("Little Indian\n");

Could you write a C program to reverse a character string using pointers, without using any library such as <string.h>?

#include <stdio.h>

// Function to calculate the length of a string
int Str_len(char *str) {
    int length = 0; // Initialize length counter

    // Loop through the string until null terminator is encountered
    while (*str != '\0') {
        length++; // Increment length for each character
        str++;    // Move to the next character in the string
    return length; // Return the calculated length

int main() {
    char str[] = "devilal"; // Input string
    // Calculate the length of the input string using Str_len function
    int len = Str_len(str);
    // Create a character array to store the reversed string
    char Reverse[len];
    printf("Length of the string: %d\n", len); // Print the length of the string
    int count = len - 1; // Initialize the counter for the reversed string
    // Loop through the original string and store characters in reverse order
    for (int i = 0; i < len; i++) {
        Reverse[i] = str[count]; // Store the character at index 'count' in 'Reverse'
        count--; // Decrement 'count' to move to the previous character in the original string
    printf("Reversed string: %s\n", Reverse); // Print the reversed string
    Reverse[len] = '\0'; // Add null terminator at the end of the reversed string
    return 0;


  • The Str_len function calculates the length of a string by iterating through it character by character until the null terminator (‘\0’) is encountered. It returns the length of the string.
  • In the main function, the input string “devilal” is defined.
  • The length of the input string is calculated using the Str_len function and stored in the variable len.
  • An array named Reverse of size len is created to store the reversed string.
  • The original string is iterated in reverse order, and each character is stored in the Reverse array.
  • Finally, the reversed string is printed, and a null terminator is added at the end to signify the end of the string.

Can you write a C function to toggle a specific bit in a given number?

#include <stdio.h>
#include <stdint.h>

// Function to toggle a specific bit in a given number
uint32_t toggleBit(uint32_t num, int pos) {
    return num ^ (1 << pos);

int main() {
    uint32_t num = 0xAAAAAAAA; // Example value
    int pos = 3; // Bit position to toggle

    printf("Original number: 0x%X\n", num); // Print original number in hexadecimal format

    // Toggle the bit at the specified position
    uint32_t toggledNum = toggleBit(num, pos);

    printf("Toggled number: 0x%X\n", toggledNum); // Print toggled number in hexadecimal format

    return 0;


  • This program defines a function toggleBit that takes a 32-bit unsigned integer num and an integer pos indicating the bit position to toggle. It returns the result after toggling the bit at the specified position.
  • In the main function, an example value num (0xAAAAAAAA) and a bit position pos (3) are used.
  • The toggleBit function is called with these values, and the result is stored in toggledNum.
  • The original and toggled numbers are printed in hexadecimal format for visualization.

By Devilal

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