3.17. Activecode Exercises

Answer the following Activecode questions to assess what you have learned in this chapter.

Q1

Question

Fix the errors in the code below so that it returns the area of a circle with radius r. Use cmath functions to get an accurate value for pi.

Example functions_a1q

double area(int r) {
    constexpr double pi = sin(1.0);
    double area = pi * r ^ 2;
    return area;
}

Answer

Below is one way to fix the program. C++ doesn't use the ^ operator for exponents. We can get the square of r by multiplying it by itself.

Example functions_a1a

#include <cmath>

double area(double r) {
    constexpr double pi = 4*atan(1.0);
    double area = pi * r * r;
    return area;
}

Q2

Fix the code below so that it prints "2 elephants".

Example functions_a2

#include <iostream>
using namespace std;

void print_animals(string a, int b) {
    cout << b << a;
}

int main () {
    // DO NOT MODIFY ANYTHING BELOW THIS LINE
    print_animals(2, "elephants");
}

Q3

Question

Fix the code below so that it prints 12 / 8 = 1.5.

Example functions_a3q

#include <iostream>

void divide (int a, int b) {
    cout << a / b;
}

int main () {
    int a = 8;
    int b = 12;

    // DO NOT MODIFY ANYTHING BELOW THIS LINE
    cout << b << " / " << a << " = "; divide (a, b);
}

Answer

Below is one way to fix the program. It's crucial that you input your arguments in the correct order so as to avoid a semantic error. Also, it's important that you understand that when you divide two integers... you will get an integer as a result.

Example functions_a3a

#include <iostream>

void divide (double a, double b) {
    std::cout << a / b;
}

int main () {
    int a = 8;
    int b = 12;
    std::cout << b << " / " << a << " = "; divide (b, a);
}

Q4

Finish the code below so that it calculates the common log of a minus the natural log of a and returns the difference. You will need to use cmath functions.

Example functions_a4

double log_subtract (double a) {

    return difference;
}

int main () {
    // DO NOT MODIFY ANYTHING BELOW THIS LINE
    cout << "Testing with a = 8..." << '\n';
    cout << "    Your solution has difference = ";
    log_subtraction(8);
    cout << '\n';
    cout << "    The correct solution has difference = -1.17635" << '\n';
    cout << "Testing with a = -2..." << '\n';
    cout << "    Your solution has difference = "; log_subtraction(-2);
    cout << '\n';
    cout << "    The correct solution has difference = nan";
}

Q5

Question

Finish the code below so that it prints "First Line", a border, and "Second Line." on three separate lines.

Example functions_a5q

#include <iostream>
using namespace std;

void border () {
    cout << "------------\n";
}

int main () {
    // Write some code below to call the function appropriately

}

Answer

Below is one way to complete the program.

Example functions_a5a

#include <iostream>
using std::cout;

void border () {
    cout << "------------\n";
}

int main () {
    cout << "First Line.\n";
    border();
    cout << "Second Line.\n";
}

Q6

Write a function called int_division that takes two doubles as parameters and returns the quotient of the integer division of the first number divided by the second. Be sure to include any necessary headers.

Example functions_a6

int int_division () {

    return quotient;
}

Q7

Question

Write a function called gpa_boost that returns your GPA rounded up to the nearest whole value. If your GPA is already at the nearest whole value, then there is no rounding. Be sure to include any necessary headers.

Example functions_a7q

double gpa_boost () {

}

Answer

Below is one way to complete the program. I used the ceil <math/ceil> function from the ``cmath` library, but you could have solved this problem without using any functions from cmath.

Example functions_a7a

#include <cmath>

double gpa_boost (double gpa) {
    return ceil(gpa);
}

Q8

Write a function called volume_prism that takes three double side-lengths as parameters, and returns the volume of a the rectangular prism. Be sure to include any necessary headers.

Example functions_a8

volume_prism ();

Q9

Question

Write a function called tan_degrees that returns the tangent of an angle given as a double in degrees. Use 3.14159 for pi. Be sure to include any necessary headers.

Example functions_a9q

tan_degrees ();

Answer

Below is one way to complete the program. You need to make sure to convert your angle to radians before doing any calculations with trigonometric functions.

Example functions_a9a

#include <cmath>

namespace mesa {
    constexpr double pi = 3.14159;

    double deg_to_radian (double degrees) {
       return degrees * (pi / 180);
    }
}

double tan_degrees (double degrees) {
    double radians = mesa::deg_to_radian(degrees);
    return tan(radians);
}

Q10

Write a function called volume_sphere that takes a double radius as a parameter and returns the volume of a sphere with the provided radius. Use 3.14159 for pi. Be sure to include any necessary headers.

Example functions_a10

volume_sphere ();