Revew OOP244 - Conversion Operators

The form of a conversion operator declaration is

 operator dataType() const;

example: operator int() const;


In our case, the compiler fails to find an exact, promoted,
      or standard-conversion match for any argument-parameter pair,
      and searches the single argument constructors for a derived data
      type conversion match.  The compiler inserts the
      constructor code to convert 1234 to a
      Student and then calls the assignment
      operator that receives a Student as
      its right operand.  That is,
harry = 1234; // calls operator=(const Student& Student(1234))
      

If the Student(int) constructor were absent, the compiler could not convert 1234 to a Student and would reject the assignment expression. However, if our class declaration had a Student(long long) constructor, the compiler could convert 1234 to 1234LL, then convert 1234LL to a Student data type, and finally assign the right Student operand to the left Student operand.

To comprehend above please refer more detail