Chapter 02 - Introduction to C++ - Challenges

Displaying variable value

Develop an application that defines a variable of type integer and displays its value. Change the value after displaying it and display the updated value.

Invoice VAT

Create an application that determines the 21% VAT (BTW) of a given number (floating point). Display both the value with and without VAT like you would see on an invoice. Use a second variable to store the actual VAT value.

Can you change the application so the number is requested from the user. Checkout http://www.cplusplus.com/doc/tutorial/basic_io/ for more info on input and input to STDOUT and from STDIN.

Generating random numbers

Checkout the following code: http://www.dreamincode.net/forums/topic/14057-producing-random-numbers/

Is uses some functions and libraries to generate random numbers.

Now change the code to print out 10 random numbers while calculating the sum and average of the randomly generated numbers.

Use a for-loop construct for this (see chapter C++ Language Constructs).

Side effects

Can you guess the output of the following construct:

    int counter = 0;
    if (true && counter++) {
        std::cout << "Counter: " << counter << std::endl;
    }
    std::cout << "Counter: " << counter << std::endl;

Roots of a Quadratic Equation

The code below should determine the roots of a quadratic equation. However there are some syntax errors and maybe even a bug in the code. Fix the code so its compiles and works correctly. Also make sure that the output is consistent.

#include <iostream>
#include <cmath>

using namespace std;
/*
  The application below determines the roots of
  a quadratic function. Just fill in the 3 coefficients.
/
int main() {
    double a, b, c;

    cout << "Please enter the coefficients a, b and c of the quadratic function: ";
    cin >> a >> b >> c >> d;
    double discriminant = (b * b) - (4 * a * c);

    if (abs(discriminant) <= 0.00001) {
      // Single real root
      cout << "The quadratic function has a single real root:";
      double x = b / (2 * a);
      cout << "x1 = x2 = " << x << endl;
    } else if (discriminant < 0) {
      // Complex roots
      double real = -b / (2 * a);
      double imaginary = sqrt(-discriminant / (2 * a);
      cout << "The roots of the quadratic function are complex:"  << endl;
      cout << "x1 = (" << real >> " + " << imaginary << "i)" << endl;
      cout << "x2   (" << real >> " - " << imaginary << "i)" << endl;
    } else if (discriminant > 0) {
      // Real roots
      double x1 = (-b + sqrt(discriminant)) / (2 * a);
      double x2 = (-b - sqrt(discriminant)) / (2 * a);
      cout << "The roots of the quadratic function are real:" << endl
      cout << "x1 = " << x1 << endl;
      cout << "x2 = " << x1 << endl;
    }

    return 0;
}

Challenges