In C++ classes, a default constructor is defined as a constructor that can be called with how many explicit arguments?

Introduction / Context:
Constructors are special member functions in C++ that initialise objects when they are created. Among them, the default constructor plays a particularly important role because it allows objects to be created without providing any arguments at the call site. Understanding what qualifies as a default constructor is essential for topics such as automatic object creation, container classes, and aggregate initialisation. This question asks you to focus on how many explicit arguments a default constructor accepts by definition.

Given Data / Assumptions:

• The language is standard C++.
• We are talking about default constructors in classes.
• A default constructor is one that can be invoked without passing any arguments in the object creation expression.
• Constructors may have parameters with default values, but the key property is whether a call can be made with no arguments.

Concept / Approach:
In C++, a default constructor is defined as a constructor that can be called with no arguments. This includes a constructor that has no parameters at all, as well as a constructor whose parameters all have default values so that the caller does not need to supply any arguments. In either case, from the caller perspective, there are zero explicit arguments in the constructor call. Therefore, when the question asks how many arguments a default constructor accepts, the correct interpretation is that it accepts zero explicit arguments at the point of invocation.

Step-by-Step Solution:
Step 1: Recall the formal definition: a default constructor is a constructor that can be called without any arguments. Step 2: Consider the simplest form, a constructor declared with an empty parameter list, such as Example(). When an object is created with Example obj;, the call uses no arguments. Step 3: Consider a constructor with parameters that all have default values, for example Example(int x = 0). This constructor can still be invoked as Example obj; without providing any explicit argument. Step 4: In both cases, from the caller side, the number of explicit arguments supplied is zero, which matches the definition used in the question. Step 5: Therefore, the correct choice is the option that states zero arguments or no parameters.

Verification / Alternative check:
You can verify this by thinking about how standard library containers behave. Many containers require that the stored type have a default constructor so that they can create arrays of objects or resize themselves without needing explicit arguments. When a vector of Example is resized, it constructs new Example objects by calling the default constructor without any arguments, which confirms that a default constructor is one that is callable with a zero argument call expression.

Why Other Options Are Wrong:
Option One argument: A constructor that always requires one explicit argument is not a default constructor, although it may be an overloaded constructor. Option Two arguments: Similarly, a constructor that needs two explicit arguments cannot be invoked with an empty call and so does not qualify as a default constructor. Option Three arguments: A constructor that always expects three explicit arguments also fails the requirement of being callable without arguments.

Common Pitfalls:
A typical confusion arises when constructors have parameters with default values. Some learners think that such constructors cannot be default constructors because parameters are present, but the true test is whether a call with no arguments is valid. Another pitfall is to confuse the term default constructor with copy constructor or parameterised constructor. Remember that the word default here refers to the absence of explicit arguments in the call expression, not to any default value of member variables.

Final Answer:
A default constructor in C++ can be called with Zero arguments (no parameters).