C++ Interview Questions – Data Types

1. [Asked in Infosys] What are data types in C++?

Answer:
Data types in C++ define the type of data a variable can store. C++ supports primitive, derived, and user-defined data types.

Categories of Data Types:

• Primitive Data Types – int, float, double, char, bool
• Derived Data Types – array, pointer, reference
• User-Defined Data Types – struct, class, enum, union

Example:

int num = 10;
float price = 9.99;
char grade = 'A';
bool isAvailable = true;

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2. [Asked in TCS] What is the difference between int, float, and double in C++?

Answer:

Data Type	Size	Precision	Example
int	4 bytes	No decimal	int a = 10;
float	4 bytes	~6 decimal places	float pi = 3.1415;
double	8 bytes	~15 decimal places	double pi = 3.1415926535;

Example:

int a = 5;
float b = 5.12f;
double c = 3.1415926535;

Note: Use double for high precision calculations.

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3. [Asked in Cognizant] What is the difference between char and string in C++?

Answer:

Feature	char	string
Stores	Single character	Sequence of characters
Header File	None	<string>
Example	char ch = 'A';	string name = "Alice";

Example:

#include <iostream>
#include <string>
using namespace std;

int main() {
    char letter = 'A';
    string name = "Alice";
    cout << "Letter: " << letter << ", Name: " << name;
    return 0;
}

Output:

Letter: A, Name: Alice

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4. [Asked in Wipro] What is the bool data type in C++?

Answer:
bool is a boolean data type that stores true (1) or false (0).

Example:

bool isPassed = true;
bool isFailed = false;
cout << isPassed;  // Output: 1
cout << isFailed;  // Output: 0

Use Case: Boolean values are commonly used in conditional statements and loops.

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5. [Asked in IBM] What are derived data types in C++?

Answer:
Derived data types are created using primitive types.

Types of Derived Data Types:

• Arrays – Collection of elements (int arr[5];)
• Pointers – Store memory addresses (int *ptr;)
• References – Alias for a variable (int &ref = num;)

Example of Derived Data Types:

int arr[3] = {1, 2, 3}; // Array
int *ptr = &arr[0]; // Pointer
int &ref = arr[1]; // Reference

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6. [Asked in Deloitte] What is the difference between signed and unsigned integers in C++?

Answer:

Type	Size	Value Range
signed int	4 bytes	-2,147,483,648 to 2,147,483,647
unsigned int	4 bytes	0 to 4,294,967,295

Example:

signed int x = -10;
unsigned int y = 100;

Use unsigned integers when negative values are not required (e.g., age, count).

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7. [Asked in Amazon] What is the difference between enum and const in C++?

Answer:

Feature	enum (Enumeration)	const (Constant)
Purpose	Defines named constants	Declares constant values
Memory Usage	Uses integer representation	Direct value storage
Example	enum Color {Red, Blue, Green};	const int PI = 3.14;

Example Using enum:

enum Color {Red, Blue, Green};
Color c = Blue;
cout << c;  // Output: 1

Example Using const:

const int pi = 3.14;

Use enum for grouping related constants, const for defining fixed values.

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8. [Asked in Microsoft] What is the auto keyword in C++?

Answer:
The auto keyword automatically detects the variable’s data type at compile time.

Example:

auto num = 10;   // int
auto pi = 3.14;  // double
auto name = "Alice"; // const char*

Use auto to simplify variable declaration and improve readability.

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9. [Asked in Google] What is nullptr in C++? How is it different from NULL?

Answer:

• nullptr (C++11 and later) – A type-safe null pointer.
• NULL (C-style) – Typically defined as 0 and can cause ambiguity in function overloading.

Example:

int *ptr1 = NULL;  // C-style
int *ptr2 = nullptr;  // Modern C++

Use nullptr in modern C++ for better type safety.

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10. [Asked in Flipkart] What is the size of different data types in C++?

Answer:

Data Type	Size (in bytes)
char	1
int	4
float	4
double	8
bool	1
void	0

Example:

cout << "Size of int: " << sizeof(int) << " bytes";
cout << "Size of double: " << sizeof(double) << " bytes";

Output (depends on system):

Size of int: 4 bytes
Size of double: 8 bytes

Use sizeof() to determine the size of a data type dynamically.