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C++ Interview Questions

Author: Paolo Miguel Besabella

C++ is one of the most widely used programming languages and has a reputation for being hard to learn. C++ first appeared in 1982 as an extension to the popular C language. It is fast, feature-rich, and reliable.

If you are preparing to interview for a programming position using C++, here are some typical questions that may be asked. Some of these questions can also be asked in Java as well as C# interviews.

What is the difference between a class and an object?

Classes and objects usually work together to solve problems. The class defines the data structure which contains the methods that operate on the data. The objects hold the raw data and provide a way for data changes to reflect themselves in other parts of a system.

The key to answering this question is to stress the relationship between a class and an object. One cannot exist without the other.

What is encapsulation?

Encapsulation is a way of hiding data within a class. This prevents different parts of a system from stepping on each others’ toes and keeps everything in its proper place. Encapsulation allows any developer to modify or add new functionality without causing conflicts with existing classes and existing functions (methods).

To answer this question, simply describe how encapsulated data can be hidden within a class; therefore, preventing accidental modification by outside forces.

What does it mean when we say that “C++ is not pass-by-value but pass-by-reference”?

This means that instead of passing one copy of data to a method, the variable name is actually passed to the function. This allows functions to update data in place instead of returning new values.

What is an abstract class and what purpose does it serve?

An abstract class serves as a template for derived classes and must contain one or more methods that can be overridden by derived classes. Abstract classes cannot instantiate objects but can be used to design complex systems with inherited hierarchies of functionality.

The advantage of using an abstract class is that it provides a way for developers to write code without having all the details about how items will work together. Instead, this information is deferred until later in development when concrete implementations are written based on each other’s interfaces from their base classes.

Why is C++ such a widely used language?

C++ emerged as a very popular language for cross-platform development and remains so today. It also has multiple implementations that conform to the standard which helps its adoption rate. For example, there is GNU’s GCC compiler for Unix and Linux, Microsoft Visual C++ and Borland C++ Builder available for Windows and Java1 for Mac OSX and Linux. ## Why do we use header files in C++?

Header files contain common definitions between libraries or groups of source code modules. The purpose of header files is to remove redundancy from many different source files by consolidating all common declarations into one header file. This makes it easier to maintain large systems with complex dependencies between various parts of the system.

Why do we use classes in C++?

Classes help solve problems by grouping data with related functions together under one name or namespace. The class provides a way for developers to write code without having all the details about how items will work together. Instead, this information is deferred until later in development when concrete implementations are written based on each other’s interfaces from their base classes.

What is the difference between an abstract class and an interface?

Interfaces are used to define contract or method signatures for derived classes. Unlike abstract classes, interfaces cannot instantiate objects but can be used to design complex systems with inherited hierarchies of functionality.

The advantage of using an interface is that it provides a way for developers to write code without having all the details about how items will work together. Instead, this information is deferred until later in development when concrete implementations are written based on each other’s interfaces from their base classes.

How can you convert a string into an integer in C++?

The most common method of converting a string into an integer is by using the atoi or strtol function. They take a string and extract an integer from it. The two functions differ only in how they treat whitespace characters (characters that fall between tokens, such as spaces and tabs). The strtol function interprets those as part of the number, while atoi does not. There are also functions to convert a string into a floating point number such as atof or strtod.

How can you convert a string into a floating-point number in C++?

The most common method of converting a string into a floating-point number is by using the atof or strtod function. Both take a string and extract a floating-point number from it, but they differ slightly in how they treat whitespace (characters that fall between tokens, such as spaces and tabs). The strtod function interprets those as part of the number, while atof does not. There are also functions to convert it into an integer like atoi or strtol.

Final Thoughts on C++ Interview Questions

It is very important to understand the process of designing and implementing an object-oriented program. This involves choosing a proper programming paradigm, which in turn depends on the problem domain and other factors.

For example, if we need to solve a particular business problem and we know that objects and classes will help fulfill it then we can use C++ as our programming language. Also, C++ allows us to use abstract base classes for design patterns such as singleton or factory or observer or others.

Finally, it is important to understand how pointers and references work because they are used in the implementation of many design patterns. For example, when we inherit from a base class in C++, we need to understand what is happening with the virtual function table and how functions are resolved at runtime.

Good knowledge of memory management and object-oriented concepts will make you a more valuable developer in any kind of project.