Which one of the following is not a valid reserved keyword in C++?

Question

Accepted Answer

The correct option is (3):
The term 'implicit' is a concept used to describe the automatic type conversion or function call that the C++ compiler performs by default, such as a single-argument constructor allowing for implicit conversion. However, **implicit** itself is not a reserved keyword in the C++ programming language standard. It is an English word used to describe an existing behavior, and the compiler does not reserve it as a special identifier. Therefore, unlike the other options which have a specific syntax-defining role, 'implicit' is the word that is not part of the C++ reserved word list.

The incorrect option is (1):
**explicit** is a valid and crucial reserved keyword in C++. Its primary role is to modify constructors that take a single argument to prevent *implicit* conversions. By marking a constructor as `explicit`, the programmer forces the object creation to be done using only direct initialization, which is a key tool for avoiding unintended type-casting errors and maintaining strong type safety in C++ code. As it is a functional part of the language's syntax, it cannot be used for any other purpose.

The incorrect option is (2):
**public** is an absolutely fundamental reserved keyword in C++, serving as one of the three primary *access specifiers* for class and struct members. When a member is declared `public`, it means that any code outside of the class, including derived classes and unrelated functions, can directly access and modify that member. It defines the external interface of a class and is indispensable for the compilation and structural integrity of C++ programs.

The incorrect option is (4):
**private** is another essential reserved keyword in C++, acting as an *access specifier*. It is the strictest access level, ensuring that any member declared after it can only be accessed or modified by the member functions of that specific class itself, or by its designated friends. This enforces the core Object-Oriented Programming (OOP) principle of **Encapsulation**, hiding implementation details from the rest of the program and protecting internal data.