Data members and member functions in C++ - Step-by-Step Execution

Concept Flow - Data members and member functions

Create Object

↓

Allocate Data Members

↓

Call Member Function

↓

Access/Modify Data Members

↓

Return or Output Result

↓

End

This flow shows how an object is created with data members, then member functions are called to access or change those data members, and finally results are returned or output.

Execution Sample

C++

class Box {
  int length;
public:
  void setLength(int l) { length = l; }
  int getLength() { return length; }
};

Defines a class Box with a data member length and member functions to set and get its value.

Execution Table

Step	Action	Data Member 'length'	Output
1	Create object b of class Box	undefined (not set)
2	Call b.setLength(10)	length = 10
3	Call b.getLength()	length = 10	10
4	End of program	length = 10

💡 Program ends after getting length value 10 from object b

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
length (data member)	undefined	10	10	10

Key Moments - 2 Insights

Why is 'length' undefined before calling setLength?

Because data members are not automatically initialized; setLength assigns the value (see execution_table step 2).

How does getLength access the data member?

getLength returns the current value of 'length' stored in the object (see execution_table step 3 output).

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'length' after step 1?

A undefined

B 10

C 0

D Not declared

💡 Hint

Check the 'Data Member length' column at step 1 in the execution_table.

At which step does 'length' get assigned the value 10?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Action' and 'Data Member length' columns in the execution_table.

If we call getLength() before setLength(), what would be the output?

A 10

B undefined or garbage value

C 0

D Compilation error

💡 Hint

Refer to variable_tracker and understand that 'length' is not initialized before setLength is called.

Concept Snapshot

class ClassName {
  data members (variables);
public:
  member functions to access/modify data members;
};
Create object, then use member functions to work with data members.

Full Transcript

This example shows a class named Box with a data member called length. When we create an object b of Box, length is not set yet. We call setLength(10) to assign 10 to length. Then getLength() returns the stored value 10. Data members hold the object's data, and member functions let us safely access or change that data. Without calling setLength first, length would be undefined. This step-by-step trace helps understand how data members and member functions work together in C++.