ProgramGuru

Create Student Objects

Create Student Objects

A class defines state and behavior for its objects.

Each StudentRecord instance can store a separate mark while exposing a consistent report operation.

Before this lesson, review Distinguish Copying from Transfer when needed.

What you’ll learn

  • Use classes and objects to create Student Objects.
  • Explain how the complete example produces 72.
  • Make the practice change and explain why the result changes or stays the same.

Follow a complete C++ example

Each StudentRecord instance can store a separate mark while exposing a consistent report operation.

Read the declarations above main before tracing its statements. Each declared name supplies the value, type or operation used later. The std:: prefix selects a name from the standard library, and cout << sends a value to the output stream.

C++17 · main.cpp · complete program

#include <iostream>

class StudentRecord  {
  int marks_;
  public: explicit StudentRecord(int marks) : marks_(marks)  {
  }
  int mark() const  {
    return marks_;
  }
}
;
int main()  {
  StudentRecord student(72);
  std::cout << student.mark() << '\n';
  return 0;
}

Expected output

72
Run in C++ compiler →

Connect the code to its result

C++17 · source used in this explanation

#include <iostream>

class StudentRecord  {
  int marks_;
  public: explicit StudentRecord(int marks) : marks_(marks)  {
  }
  int mark() const  {
    return marks_;
  }
}
;
int main()  {
  StudentRecord student(72);
  std::cout << student.mark() << '\n';
  return 0;
}

Expected output

72

A class defines state and behavior for its objects. Each StudentRecord instance can store a separate mark while exposing a consistent report operation.

Trace the result: Read the complete program below from its starting values to the output operations. Each std::cout statement displays the value supplied at that point; \n begins the next line. The resulting lines, in order, are 72. In this example, distinguish what the program calculates or changes from what it actually displays.

Important mistakes and boundaries

A class is a definition; an object is a particular instance. Avoid using one shared static field for a value meant to differ by student.

Change the school example

C++17 · edit this complete example

#include <iostream>

class StudentRecord  {
  int marks_;
  public: explicit StudentRecord(int marks) : marks_(marks)  {
  }
  int mark() const  {
    return marks_;
  }
}
;
int main()  {
  StudentRecord student(72);
  std::cout << student.mark() << '\n';
  return 0;
}

Your task: Construct the student with 80. Before running your edited program, predict the new output and explain which stored value, condition or object changes. Keep the rest of the example intact.

Use the complete source repeated here; this task does not depend on remembering code from another section.

Worked answer and reasoning

Worked variation: Construct the student with 80. Its report returns 80.

A class defines state and behavior for its objects. Each StudentRecord instance can store a separate mark while exposing a consistent report operation.

A class is a definition; an object is a particular instance. Avoid using one shared static field for a value meant to differ by student.

For a baseline run, save this source as main.cpp and use clang++ -std=c++17 -Wall -Wextra -pedantic main.cpp -o school, or equivalent g++ flags. Recompile after editing so that you run the updated executable.

The source and output below belong to the edited program. Compare them with the original example to see the consequence of this single change.

C++17 · worked variation · complete program

#include <iostream>

class StudentRecord  {
  int marks_;
  public: explicit StudentRecord(int marks) : marks_(marks)  {
  }
  int mark() const  {
    return marks_;
  }
}
;
int main()  {
  StudentRecord student(80);
  std::cout << student.mark() << '\n';
  return 0;
}

Expected output

80
Run in C++ compiler →

Check your understanding

C++17 · original program for this question

#include <iostream>

class StudentRecord  {
  int marks_;
  public: explicit StudentRecord(int marks) : marks_(marks)  {
  }
  int mark() const  {
    return marks_;
  }
}
;
int main()  {
  StudentRecord student(72);
  std::cout << student.mark() << '\n';
  return 0;
}
Before making the practice edit, what does the original C++17 program print?
Choose one answer. You can try again.

Answer and explanation

72

A class defines state and behavior for its objects. Each StudentRecord instance can store a separate mark while exposing a consistent report operation. A class is a definition; an object is a particular instance. Avoid using one shared static field for a value meant to differ by student.

What to remember

A class defines state and behavior for its objects. A class is a definition; an object is a particular instance. Avoid using one shared static field for a value meant to differ by student.

Useful connections: Distinguish Copying from Transfer, Name and Update Values.

Language and design guidance: C++ Core Guidelines and C++ working draft. The draft describes an evolving language; these examples deliberately target C++17.

Reaching the recap and completing the quizzes are separate milestones.

    Next lesson: Initialize Valid Objects →