Exercise solutions: Basics of C++

Exercise 1

The bugs are:

Exercise 2

The answers are:

Program listing:

#include <iostream >

int main ()
{
    // Program to compute result of expression
    // (a):
    std::cout << "Value = " << (7.0 * 3) / 5 << "\n";
    // answer: 4.2

    // (b):
    std::cout << "Value = " << (7 * 3) / 5 << "\n";
    // answer: 4

    // (c):
    std::cout << "Value = " << (7 * 3) % 5 << "\n";
    // answer: 1

    // (d):
    // std::cout << "Value = " << (7.0 * 3) % 5 << endl;
    // will not compile: modulo operator undefined
    // for floating point types!

    return 0;
}

Exercise 3

There was an error on line 14 - we need to force the program to use floating point arithmetic rather than integer arithmetic. The corrected code is as follows:

# include <iostream>

int main ()
{
    // program to convert distances between miles and km
    float km, miles, km_in_miles ;

    // read distance in miles
    std::cout << "Enter distance in miles: ";
    std::cin >> miles ;

    // convert to km
    km_in_miles = (5.0/8.0); // one km in units of miles
    km = miles / km_in_miles;

    // display in km
    std::cout << " This equates to " << km << " km\n";

    return 0;
}

Exercise 4

Solution:

#include <iostream>

int main ()
{
    // Program to compute result and remainder
    // using integer arithmetic

    int n, result , remainder;

    std::cout << "Enter a number: ";
    std::cin >> n;

    result = (2 + 3 * 3) / n;
    remainder = (2 + 3 * 3) % n;

    std::cout << "Result = " << result << "\n";
    std::cout << "Remainder = " << remainder << "\n";

    return 0;
}

Exercise 5

Modified solution:

#include <iostream>

int main ()
{
    // Program to compute result and remainder
    // using integer arithmetic

    int n;
    float result;

    std::cout << "Enter a number: ";
    std::cin >> n;

    result = (2.0 + 3.0 * 3.0) / n;
    remainder = (2.0 + 3.0 * 3.0) % n;

    std::cout << "Result = " << result << "\n";

    return 0;
}

Exercise 6

Solution:

#include <iostream >

int main ()
{
    int x=5, y=10;

    // (a)
    std::cout << ++x << "\n";

    // (b)
    std::cout << y-- << "\n";

    return 0;
}

Exercise 7

(a)

No compilation error, although behaviour at run-time undefined due to division by zero.

(b)

No compilation error. the std::abs() function is a template function and will return a value of the same type as its argument, i.e. an int in this case.

(c)

Compilation error. The modulus operator will only work for integer values, and this will be checked at compile-time as C++ uses static type checking.

Exercise 8

Solution (reading from terminal):

#include <cmath>
#include <cstdlib>

int main ()
{
    int n;

    std::cout << "Enter number: ";
    std::cin >> n;

    std::cout << "result = " << std::sqrt (std::abs (n)) << "\n";

    return 0;
}

Solution (using command-line argument):

#include <iostream>
#include <cmath>
#include <vector>
#include <string>
#include <stdexcept>

int main (int argc, char* argv[])
{
    std::vector<std::string> args (argv, argv+argc);

    if (args.size() < 2)
      throw std::runtime_error ("expected at least one argument");

    int n = std::stoi (args[1]);
    std::cout << "result = " << std::sqrt (std::abs (n)) << "\n";

    return 0;
}

Exercise 9

Solution:

#include <iostream>
#include <cmath>
#include <vector>
#include <string>
#include <stdexcept>

int main (int argc, char* argv[])
{
    std::vector<std::string> args (argv, argv+argc);

    if (args.size() < 4)
      throw std::runtime_error ("expected 3 arguments");

    double x = std::stod (args[1]);
    double y = std::stod (args[2]);
    double z = std::stod (args[3]);

    double result = std::pow (x, std::pow (y,z));
    std::cout << "x^y^z = " << result << "\n";

    return 0;
}

Exercise 10

Solution:

#include <iostream>
#include <cmath>
#include <vector>
#include <string>
#include <stdexcept>

int main (int argc, char* argv[])
{
    // Program to compute expression
    // using floating point arithmetic

    std::vector<std::string> args (argv, argv+argc);

    if (args.size() < 2)
      throw std::runtime_error ("expected one integer argument");

    int i = std::stoi (args[1]);

    // use decimal points in numbers to ensure
    // that floating-point arithmetic is used:
    float v = (i + 3.0) * (i + 2.0) * (i + 1.0) * i;
    float result = v * v * v;

    std::cout << "Result = " << result << "\n";
    return 0;
}

Exercise 11

The errors are:

Corrected code:

#include <iostream>
#include <cmath>

int main ()
{
    // compute roots of quadratic equation of form ax^2 + bx + c = 0

    // declare variables for coefficients and roots
    float a, b, c, r1, r2;

    // read values of coefficients from user
    std::cout << "Enter a b c: ";
    std::cin >> a >> b >> c;

    // compute roots
    r1 = ( -b + std::sqrt (b*b - 4.0*a*c) ) / (2.0*a);
    r2 = ( -b - std::sqrt (b*b - 4.0*a*c) ) / (2.0*a);

    // display answers
    std::cout << "Roots = " << r1 << ", " << r2 << "\n";
    return 0;
}

Exercise 12

Solution:

#include <iostream>
#include <cmath>

int main ()
{
    float a, b, c;
    std::cout << "Enter the values of a b c: ";
    std::cin >> a >> b >> c;

    float s = (a + b + c) / 2.0;
    float area = std::sqrt (s * (s - a) * (s - b) * (s - c));

    std::cout << "The area of the triangle is " << area << "\n";
    return 0;
}

Exercise 13

Solution:

#include <iostream>
#include <cmath>
#include <vector>
#include <string>
#include <stdexcept>

int main (int argc, char* argv[])
{
    // Program to compute expression
    // using floating point arithmetic

    std::vector<std::string> args (argv, argv+argc);

    if (args.size() < 2)
      throw std::runtime_error ("expected one floating-point argument");

    float r = std::stod (args[1]);

    // compute area , vol
    float area = 4.0 * M_PI * r * r;
    float vol = (4.0 / 3.0) * M_PI * r * r * r;

    // display to terminal:
    std::cout << "Surface area = " << area << "\n";
    std::cout << "Volume = " << vol << "\n";

    return 0;
}