Parameterized constructor in C++ - Step-by-Step Execution

Concept Flow - Parameterized constructor

Create object

↓

Call constructor with parameters

↓

Assign parameters to object variables

↓

Object initialized with given values

↓

Object ready to use

When an object is created, the parameterized constructor runs, taking input values and setting the object's variables.

Execution Sample

C++

class Box {
  int length;
public:
  Box(int l) { length = l; }
  int getLength() { return length; }
};
Box b(5);

This code creates a Box object with length set to 5 using a parameterized constructor.

Execution Table

Step	Action	Parameter value	Variable 'length' value	Output
1	Call constructor Box(5)	5	uninitialized
2	Assign length = 5	5	5
3	Constructor ends	5	5
4	Call b.getLength()		5	5

💡 Constructor finishes after assigning parameter to length; getLength() returns 5.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
length	uninitialized	uninitialized	5	5
parameter l	N/A	5	5	N/A

Key Moments - 2 Insights

Why does 'length' have the value 5 after the constructor runs?

Because in step 2 of the execution_table, the parameter 'l' with value 5 is assigned to the member variable 'length'.

What happens if we create Box b(10)?

The constructor assigns 10 to 'length' instead of 5, similar to step 2 but with parameter value 10.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'length' after step 2?

A uninitialized

B 0

C 5

D undefined

💡 Hint

Check the 'Variable length value' column in row for step 2.

At which step does the constructor finish running?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look at the 'Action' column describing constructor end.

If we change the parameter to 7 when creating Box b(7), what will getLength() return?

A 5

B 7

C 0

D uninitialized

💡 Hint

Refer to variable_tracker and how parameter value assigns 'length'.

Concept Snapshot

Parameterized constructor syntax:
class ClassName {
  Type var;
public:
  ClassName(Type param) { var = param; }
};
Creates object with var set to param value.

Full Transcript

A parameterized constructor is a special function in a class that runs when an object is created. It takes input values (parameters) and uses them to set the object's variables. For example, when we create a Box object with Box b(5), the constructor receives 5 and assigns it to the length variable. This way, the object starts with the values we want. The execution steps show calling the constructor, assigning the parameter to the variable, and then using the object. This helps us create objects with different starting values easily.