10-02 Lecture 09 & 10

Prerequisites

Before going over the practice problems, please review these sections

* Note that 2. Program structure/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.

General Problems

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] << ", ";
}

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;

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!";
	}
}

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 << "]";
}

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;
}

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;
}

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);

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";

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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