12. Week 6 Thursday: Practise with Functions
≪ 11. Week 6 Tuesday: Functions | Table of Contents | 13. Week 7: Midterm ≫Today’s class was focused on reviewing the homework, which was centred around writing our own functions in the context of larger problems.
Functions are a difficult part of the learning curve, and practise makes perfect. To that end, here’s a few practise problems that will (hopefully) help you get more familiar with functions, particularly with understanding how the computer processes code that’s been split across different functions.
Problem 1.
Determine the output of the following code:
1#include <iostream>
2
3using namespace std;
4
5void foo(int n) {
6 for(int i = 0; i < n; i++) {
7 cout << i << " ";
8 }
9
10 cout << endl;
11}
12
13void bar(int n) {
14 for(int i = 0; i < n; i++) {
15 if(i % 2 == 0) {
16 continue;
17 }
18
19 foo(i);
20 }
21}
22
23int main() {
24 cout << "The output of bar(5) is as follows: " << endl;
25 bar(5);
26 return 0;
27}
Problem 2.
Determine the output of the following code.
1#include <iostream>
2#include <string>
3
4using namespace std;
5
6double gas(char c, string s) {
7 if(s.length() == 0) {
8 return 0;
9 }
10
11 double d = 1.0 / s.length();
12 double e = 0;
13 for(int i = 0; i < s.length(); i++) {
14 if(s.at(i) == c) {
15 e += d;
16 }
17 }
18
19 return e;
20}
21
22void wire(string s) {
23 double d = -1;
24 for(int i = 0; i < s.length(); i++) {
25 double e = gas(s.at(i), s);
26 if(e > d) {
27 s.at(i) = '#';
28 d = e;
29 }
30 }
31
32 cout << s << endl;
33}
34
35int main() {
36 wire("Hello world!");
37 wire("Functions make perfect sense to me.");
38 wire("I changed my mind.");
39 return 0;
40}
Problem 3.
A student is trying to solve the following problem:
Write a C++ program that takes an integer \(n\) as input, followed by \(n\) strings (with no spaces). If a string contains any digits, replace the whole string with asterisks. Print out the user’s modified input, one word per line.
Sample Run:
INPUT 4
INPUT I made $15.49 today
OUTPUT I
made
******
today
INPUT 4
INPUT My office is MS2943
OUTPUT My
office
is
******
Below is the code the student came up with. Identify the errors, if there are any, and fix them.
1#include <iostream>
2#include <string>
3
4using namespace std;
5
6// replaces a string with all asterisks
7void censor_string(string s) {
8 for(int i = 0; i < s.length(); i++) {
9 s.at(i) = '*';
10 }
11}
12
13// determines if a string has any digits or not
14void has_digits(string s) {
15 for(int i = 0; i < s.length(); i++) {
16 if('0' <= s.at(i) && s.at(i) <= '9') {
17 return true;
18 } else {
19 continue;
20 }
21 }
22
23 return false;
24}
25
26int main() {
27 int n;
28 cin >> n;
29
30 for(int i = 0; i < n; i++) {
31 string input;
32 cin >> input;
33
34 if(has_digits(input)) {
35 cout << censor_string(s) << endl;
36 }
37 }
38
39 return 0;
40}