6.9. Activecode Exercises¶

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

Question

Fix the code below so that it prints "THE TEAM" "THE TEAM" "THE TEAM" on three separate lines.

Example cond_rec_a1q

 1#include <iostream>
 2
 3x = 8;
 4y = 8;
 5
 6if (x % 2 == 0) {
 7    std::cout << "THE TEAM";
 8} else if (x >= y) {
 9    std::cout << "THE TEAM";
10} else if (y >= x) {
11    std::cout << "THE TEAM";
12}

Answer

Below is one way to fix the program. Since we want "THE TEAM" to print three times, we must check all three conditons. this means changing the else if statements to if statements.

Example cond_rec_a1_a

 1#include <iostream>
 2
 3x = 8;
 4y = 8;
 5
 6if (x % 2 == 0) {
 7    std::cout << "THE TEAM\n";
 8}
 9if (x >= y) {
10    std::cout << "THE TEAM\n";
11}
12if (y >= x) {
13    std::cout << "THE TEAM\n";
14}

You are part of a class where everyone passes, but it's very hard to pass with an A. Fix the function so it prints your letter grade according to this scheme. [0, 50) = C, [50, 85) = B, and [85, 100] = A.

Example cond_rec_a2

 1#include <iostream>
 2#include <string>
 3
 4std::string which_door (double grade) {
 5    s = "";
 6    if (grade < 50) {
 7        s = "C";
 8    }
 9    if (grade < 85) {
10        s = "B";
11    }
12    if (grade >= 85) {
13        s = "A";
14    }
15    std::cout << s;
16}

Question

Fix the infinite recursion in the code below. The function should not count any numbers after 10 (the highest numbers that should print are 9 or 10). When it is done counting, the function should print that.

Example cond_rec_a3q

 1#include <iostream>
 2using std::cout;
 3
 4void count_by_2 (int num) {
 5    if (num != 10) {
 6        cout << num;
 7        count_by_2 (num + 2);
 8    }
 9    else {
10        cout << num
11             << "\n_done counting!";
12    }
13}
14
15int main () {
16    count_by_2(6);
17}

Answer

Below is one way to fix the program. The infinite recursion happens when we use an odd number as an argument. By checking that a number is less than 99, the highest numbers to recurse are 98 and 97. 98 + 2 == 100 and 97 + 2 == 99, so we never count past 100.

Example cond_rec_a3_a

 1#include <iostream>
 2using std::cout;
 3
 4void count_by_2 (int num) {
 5    if (num < 9) {
 6        cout << num;
 7        count_by_2 (num + 2);
 8    }
 9    else {
10        cout << num
11             << "\n_done counting!";
12    }
13}
14
15int main () {
16    count_by_2(6);
17}

In the following question, std::boolalpha is an I/O manipulator that replaces 'falsy' values witht he word false and 'truthy' expressions witht he word true.

Finish the code below so that it prints true if x is even and false if x is odd.

Example cond_rec_4

1#include <iostream>
2
3void is_even (int num) {
4    if (num % 2 == 0) {
5        std::cout << std::boolalpha << true;
6    }
7}

Question

Finish the code below so that the function will continue to ask for input until the user guesses the word correctly.

Example cond_rec_a5q

 1#include <iostream>
 2#include <string>
 3using namespace std;
 4
 5bool guess_word (string correct) {
 6    cout << "Guess the word!";
 7    string guess;
 8    cin >> guess;
 9    if (guess == correct) {
10        cout << "That's it!";
11    }
12}

Answer

Below is one way to complete the program.

Example cond_rec_a5a

 1#include <iostream>
 2#include <string>
 3using namespace std;
 4
 5bool guess_word (string correct) {
 6    cout << "Guess the word!";
 7    string guess;
 8    cin >> guess;
 9    if (guess == correct) {
10        cout << "That's it!";
11    }
12    else {
13        guess_word(correct);
14    }
15}

Write the function greater that prints true if the first double argument is greater than the second double argument. Be sure to include any necessary headers.

Example cond_rec_a6

1void greater () {
2
3}

Question

Write the function good_vibes that prints "I'm having a mood day!" depending on the value of mood. If mood is "bad", then the function should not do anything since it's good vibes only. Be sure to include any necessary headers.

Example cond_rec_a7q

1void good_vibes (string mood) {
2
3}

Answer

Below is one way to write the program. The return allows the function to exit if there are bad vibes in the room. Otherise, the function prints as directed.

Example cond_rec_a7a

1void good_vibes (string mood) {
2    if (mood == "bad") {
3        return;
4    }
5    cout << "I'm having a " << mood << " day";
6}

Write the function exclusive_or that prints true If either a OR b is true, and prints false otherwise. Be sure to include any necessary headers.

Example cond_rec_8

1void exclusive_or (bool a, bool b) {
2
3}

Question

Write the function countdown that takes a positive integer and decrements it until eaching zero, printing the number at each step of the way. Once it reaches zero, it should print "Blastoff!"

Example cond_rec_a9q

1void countdown (int num) {
2
3}

Answer

Below is one way to write the program.

Example cond_rec_a9a

 1void countdown (int num) {
 2    if (num != 0){
 3        cout << num << '\n';
 4        num -= 1;
 5        countdown (num);
 6    }
 7    else {
 8        cout << "Blastoff!";
 9    }
10}

Q10

Write the function print_negative that asks the user for a negative number. If the user does not provide a negative number, it should contine asking until the user provides one. It should then print the negative number.

Example cond_rec_a10

1void print_negative () {
2
3}