10-02 Lecture 09 & 10

Prerequisites

Before going over the practice problems, please review these sections

• Functions
• vector

* Note that Functions now has a tl;dr section that summarizes the content

Group Problems

Problem 1: Weekly Rainfall Analyzer

• Write a program that has a vector that stores the rainfall (in millimeters) for each day of a week and another vector for the names of the days.
• Write a function that finds all days when the rainfall is higher than the week’s average rainfall. Return a vector of the names of those days.

Objectives:

• You have rainfall measurements for each day of the week in a vector.

• Your goal is to figure out which days had rainfall higher than the average of the whole week.

• For those special days, report the name of each day.

Problem 2: Alarm Frequency Finder

Suppose you want a vector to represent hourly temperature readings for a 24-hour period. The building is equipped with an alarm that sounds whenever the temperature drops at least 10 degrees compared to the previous hour.

• Write a function to return how many alarms would sound in one 24-hour dataset.

Objectives:

• You have a vector of temperature readings, one for each hour over 24 hours.

• The building’s alarm sounds if the temperature drops by 10 degrees or more between any two consecutive hours.

• Your job is to count how many alarms would go off during the day.

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General Problems

1. Identify the logical error and explain the mistake.

vector<int> vals = {1, 2, 3, 4, 5, 6..};
for (size_t i = 0; i > vals.size(); i++) {
	cout << vals[i] << ", ";
}

2. Identify the error and explain the mistake. If there are multiple, repeat the process.

The program is expected to print out 14;

vector<int> v(10);
for (size_t i = 0; i < 10; i++) {
	v[i] = i * 2;
}
cout << v[6] << endl;

3. Modify the line to fix the error

The program is expected to find the value 19 and print out Found! Challenge: Create a line of code where it breaks after finding the value;

vector<int> numbers = {1, 5, 6, 12, 16, 21, 26, 23};
for (size_t i = 0; i < numbers.size(); i++) {
	if (numbers[i] == 19) {
		cout << "Found!";
	}
}

4. Identify the error and fix the issue.

The program doesn’t run smoothly because of this error.

int printVector(vector<int> y) {
    cout << "[";
 
    for (size_t i = 0; i < y.size(); i++) {
        if (i < y.size()-1)
            cout << ", ";
          
        cout << y[i];
    };
 
    cout << "]";
}

5. Identify the error and fix the issue.

#include <cmath>
...
 
bool isPrime(int num) {
	if (num < 0) return isPrime(abs(num));
	if (num == 1) return false;
	
	for (int i = 2; i <= sqrt(floor(num)); i++) {
		if (num % i == 0)
			return false;
	}
}
 
void printPrimeNumbers(vector<int> nums) {
	for (size_t i = 0; i < nums.size(); i++) {
		if isPrime(nums[i]) {
			cout << nums[i];
			if (i != nums.size() - 1)
				cout << ", ";
		}
	}
}
 
int main() {
	vector<int> vec;
	
	printPrimeNumbers(vec);
	
	return 0;
}

6. Making the function modify the variables

void idkWhatThisIs(int a, int b, int c) {
	c = a + b;
	a = 6;
	b = 9;
}
 
int main() {
	int a = 5, b = 4;
	int sum;
	idkWhatThisIs(a, b, sum);
	
	cout << sum;
	
	return 0;
}

7. Explain what this code does.

void doesWhatever(vector<string>& words) {
    if (!words.empty()) {
        string temp = words[0];
        words[0] = words[words.size()-1];
        words[words.size()-1] = temp;
    }
}
 
vector<string> list = {"apples", "bananas", "pears", "watermelons"};
doesWhatever(list);

8. Explain what this code does.

int countMultiples(const vector<int>& arr, int n) {
    int count = 0;
    for (size_t i = 0; i < arr.size(); i++) {
        if (arr[i] % n == 0) count++;
    }
    
    return count;
}
 
cout << countMultiples({1, 2, 3, 4, 5}, 1); " multiples";

9. Make the function return a certain value 15 without changing the arguments of the calling function

#include <iostream>
using namespace std;
 
int multiply (int a, int b) {
	return a * b;
}
 
cout << multiply(5);

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