C Inteview Questions – Introduction

1. [Asked in Infosys] What is the C programming language?

Answer:
C is a general-purpose, procedural programming language developed by Dennis Ritchie at Bell Labs in 1972. It is widely used for system programming, embedded systems, and application development.

Key Features:

• Simple and efficient – Uses a structured approach.
• Fast execution – Close to assembly language.
• Portable – Runs on various platforms.
• Rich library support – Standard library functions.

Example Use Case:

• Operating Systems (Linux, Windows kernels are written in C).

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2. [Asked in TCS] Why is C called a procedural language?

Answer:
C is called a procedural language because it follows a step-by-step approach where programs are structured into procedures (functions).

Characteristics of Procedural Programming:

• Uses functions to break down problems.
• Sequential execution of statements.
• Modular approach for better maintainability.

Example:

#include <stdio.h>
void greet() {
    printf("Hello, World!");
}
int main() {
    greet(); // Function call
    return 0;
}

Here, greet() is a procedure (function) used to print a message.

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3. [Asked in Cognizant] What are the main applications of C programming?

Answer:
C is widely used in system and application development due to its speed and efficiency.

Real-World Applications:

• Operating Systems – Linux, Windows, Unix.
• Embedded Systems – Microcontrollers, IoT devices.
• Game Development – Graphics engines.
• Database Systems – MySQL, PostgreSQL.
• Compiler Development – GCC, Clang.

Example:

• The Python interpreter (CPython) is written in C.

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4. [Asked in Wipro] What is the structure of a C program?

Answer:
A basic C program structure consists of:

Components of a C program:

1. Preprocessor Directives (#include <stdio.h>)
2. Global Declarations
3. Main Function (int main())
4. Statements and Logic
5. Return Statement (return 0;)

Example:

#include <stdio.h>  // Preprocessor Directive
int main() {        // Main Function
    printf("Hello, C!"); // Statement
    return 0;       // Return Statement
}

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5. [Asked in IBM] What is the difference between C and C++?

Answer:

Feature	C	C++
Paradigm	Procedural	Object-Oriented + Procedural
Data Security	No encapsulation	Supports encapsulation (classes)
Function Overloading	Not supported	Supported
Memory Management	Uses malloc() and free()	Uses new and delete

Example:

• C is used for OS kernels, while C++ is used for game development.

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6. [Asked in Deloitte] What are the basic data types in C?

Answer:
C has four primary data types:

Type	Size	Example
int	4 bytes	int a = 10;
float	4 bytes	float pi = 3.14;
char	1 byte	char c = 'A';
double	8 bytes	double d = 9.8765;

Example:

int num = 100;
float pi = 3.14;
char letter = 'C';
double largeValue = 9876.543;

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7. [Asked in Amazon] What are the key differences between printf() and scanf()?

Answer:

Feature	printf()	scanf()
Purpose	Outputs data	Takes user input
Format Specifiers	%d, %f, %s, %c	%d, %f, %s, %c
Return Type	Number of characters printed	Number of inputs read

Example:

#include <stdio.h>
int main() {
    int age;
    printf("Enter your age: ");  
    scanf("%d", &age);
    printf("You are %d years old", age);
    return 0;
}

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8. [Asked in Microsoft] What is a pointer in C, and why is it important?

Answer:
A pointer is a variable that stores the memory address of another variable.

Importance of Pointers:

• Efficient memory management.
• Used in data structures (linked lists, trees, etc.).
• Pass-by-reference in functions.

Example:

#include <stdio.h>
int main() {
    int num = 10;
    int *ptr = &num;  // Pointer stores the address of num
    printf("Value: %d, Address: %p", *ptr, ptr);
    return 0;
}

Output:

Value: 10, Address: 0x7ffee5b7d3a4

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9. [Asked in Google] What is the difference between while and do-while loops?

Answer:

Feature	while Loop	do-while Loop
Condition Check	Before execution	After execution
Execution Guarantee	May not execute	Executes at least once

Example:

// while loop
int i = 0;
while (i < 3) {
    printf("Hello ");
    i++;
}

// do-while loop
int j = 0;
do {
    printf("World ");
    j++;
} while (j < 3);

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10. [Asked in Flipkart] What is a typedef in C?

Answer:
typedef is used to create user-defined names for existing data types.

Benefits:

• Improves readability.
• Simplifies complex struct declarations.

Example:

typedef unsigned int UI;
UI age = 25;  // Now UI is an alias for unsigned int