C Interview Question and Answers (Part-C)

This is Part-B of commonly asked C programming language interview questions along with their answers.

What is the const pointer in C?

A const pointer is a pointer that points to a constant value. It can’t modify the value it points to.

int x = 10; 

const int *ptr = &x; // ptr is a pointer to a constant integer (can't modify x)

What is the volatile pointer in C?

A volatile pointer is a pointer that points to a volatile variable. It indicates that the value of the variable may change at any time, so the compiler should avoid optimizations related to that variable.

volatile int sensor_value; 

volatile int *ptr = &sensor_value; // ptr is a volatile pointer to an integer

Explain the typedef for function pointers in C

typedef can be used to create aliases for function pointer types to simplify their usage.

typedef int (*OperationFunc)(int, int);

int add(int a, int b) {
    return a + b;
}

int subtract(int a, int b) {
    return a - b;
}

int main() {
    OperationFunc operation;

    operation = add;
    printf("Addition: %d\n", operation(5, 3));

    operation = subtract;
    printf("Subtraction: %d\n", operation(5, 3));

    return 0;
}

What is the const function in C?

A const function is a function that promises not to modify the state of the object it is called on. The const keyword is used in the function declaration to indicate this promise.

struct Point {
    int x;
    int y;
};

void printCoordinates(const struct Point *p) {
    printf("X: %d, Y: %d\n", p->x, p->y);
}

Explain the extern keyword in C.

extern is used to declare a global variable or function that is defined in a different source file. It indicates that the variable or function is defined elsewhere

// file1.c
int globalVar = 10;

// file2.c
extern int globalVar; // Declare the variable from file1.c

int main() {
    printf("Global variable: %d\n", globalVar); // Access the global variable
    return 0;
}

What is a structure in C?

A structure is a user-defined data type that allows you to group different data types together under a single name.

struct Student {
    char name[50];
    int age;
    float gpa;
};

int main() {
    struct Student student1;
    strcpy(student1.name, "John");
    student1.age = 20;
    student1.gpa = 3.8;

    printf("Name: %s\n", student1.name);
    printf("Age: %d\n", student1.age);
    printf("GPA: %.2f\n", student1.gpa);
    return 0;
}

What are preprocessor directives in C?

Preprocessor directives are instructions to the compiler that start with #. They are executed before the actual compilation process.

#define PI 3.14159
#define SQUARE(x) ((x) * (x))

int main() {
    float radius = 2.5;
    float area = PI * SQUARE(radius);

    printf("Area of circle: %.2f\n", area);
    return 0;
}

These are more C programming language interview questions that cover topics like function pointers, structures, preprocessor directives, and usage of extern, const, volatile keywords. Remember to practice coding and understand the core concepts thoroughly to excel in C programming interviews.