Parameterized constructor in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of parameterized constructor initialization

What is the output of this C++ program using a parameterized constructor?

C++

#include <iostream>
using namespace std;

class Box {
  int length;
public:
  Box(int l) { length = l; }
  void show() { cout << length << endl; }
};

int main() {
  Box b(10);
  b.show();
  return 0;
}

A 0

B Compilation error

C Garbage value

D 10

💡 Hint

The constructor sets the length to the passed value.

The parameterized constructor sets length to 10, so show() prints 10.

❓ Predict Output

intermediate

Value of member after parameterized constructor call

What is the value of member 'width' after this code runs?

C++

#include <iostream>
using namespace std;

class Rectangle {
  int width;
public:
  Rectangle(int w) { width = w; }
  int getWidth() { return width; }
};

int main() {
  Rectangle r(15);
  cout << r.getWidth() << endl;
  return 0;
}

A Compilation error

B 0

C 15

D Undefined behavior

💡 Hint

The constructor sets width to the passed value.

The parameterized constructor assigns 15 to width, so getWidth() returns 15.

🔧 Debug

advanced

Identify the error in parameterized constructor usage

What error does this code produce when compiled?

C++

#include <iostream>
using namespace std;

class Circle {
  int radius;
public:
  Circle() { radius = 5; }
  Circle(int r) { radius = r; }
  void show() { cout << radius << endl; }
};

int main() {
  Circle c();
  c.show();
  return 0;
}

A Compilation error: 'c' is not an object

B Output: 5

C Output: 0

D Runtime error: segmentation fault

💡 Hint

Look at how 'c' is declared in main.

The line 'Circle c();' declares a function, not an object. So 'c.show()' causes a compilation error.

❓ Predict Output

advanced

Output of constructor with member initializer list

What is the output of this program?

C++

#include <iostream>
using namespace std;

class Point {
  int x, y;
public:
  Point(int a, int b) : x(a), y(b) {}
  void display() { cout << x << "," << y << endl; }
};

int main() {
  Point p(3, 4);
  p.display();
  return 0;
}

A 3,4

B 0,0

C Compilation error

D 4,3

💡 Hint

The member initializer list sets x and y to the passed values.

The constructor initializes x=3 and y=4, so display prints '3,4'.

🧠 Conceptual

expert

Behavior of parameterized constructor with default arguments

Consider this class with a parameterized constructor having default arguments. What will be the output of the program?

C++

#include <iostream>
using namespace std;

class Sample {
  int a, b;
public:
  Sample(int x = 1, int y = 2) { a = x; b = y; }
  void print() { cout << a << "," << b << endl; }
};

int main() {
  Sample s1;
  Sample s2(5);
  Sample s3(7, 8);
  s1.print();
  s2.print();
  s3.print();
  return 0;
}

A

0,0
5,2
7,8

B

1,2
5,2
7,8

C Compilation error due to ambiguous constructor calls

D

1,2
5,0
7,8

💡 Hint

Default arguments fill in missing parameters from right to left.

s1 uses defaults (1,2), s2 uses 5 and default 2, s3 uses 7 and 8.