How do I convert from arrays to STL vectors? - c++

Question

In my class we recently got introduced to STL vectors. My professor has given us a program that uses arrays, and we are to convert it to use std::vectors instead. He would like us to use iterators, so we're not allowed to use square brackets, the push_back member function, or the at member function. Here's one of the for loops from the program I have to convert:
void readData(Highscore highScores[], int size)
{
for(int index = 0; index < size; index++)
{
cout << "Enter the name for score #" << (index + 1) << ": ";
cin.getline(highScores[index].name, MAX_NAME_SIZE, '\n');
cout << "Enter the score for score #" << (index + 1) << ": ";
cin >> highScores[index].score;
cin.ignore();
}
cout << endl;
}
`
I'm just not quite understanding how to convert them. so far, I was kind of able to get this: for (vector <Highscore> :: iterator num = scores.begin(); num < scores.end(); num++)for the for loop. It doesn't quite make sense to me so I was hoping I can get some more tips or even more information on how to convert them. I don't want an answer, simply just a tip. Thank you! (if its of any help, this is the program I am having to convert and these are the four headers we have to use
void getVectorSize(int& size);
void readData(vector<Highscore>& scores);
void sortData(vector<Highscore>& scores);
vector<Highscore>::iterator findLocationOfLargest(
const vector<Highscore>::iterator startingLocation,
const vector<Highscore>::iterator endingLocation);
void displayData(const vector<Highscore>& scores);
above are the headers that have to be used (having to use these instead of the programs headers)
#include <iostream>
using namespace std;
const int MAX_NAME_SIZE = 24;
struct Highscore{
char name[MAX_NAME_SIZE];
int score;
};
void getArraySize(int& size);
void readData(Highscore highScores[], int size);
void sortData(Highscore highScores[], int size);
int findIndexOfLargest(const Highscore highScores[], int startingIndex, int size);
void displayData(const Highscore highScores[], int size);
int main()
{
Highscore* highScores;
int size;
getArraySize(size);
highScores = new Highscore[size];
readData(highScores, size);
sortData(highScores, size);
displayData(highScores, size);
delete [] highScores;
}
void getArraySize(int& size){
cout << "How many scores will you enter?: ";
cin >> size;
cin.ignore();
}
void readData(Highscore highScores[], int size)
{
for(int index = 0; index < size; index++)
{
cout << "Enter the name for score #" << (index + 1) << ": ";
cin.getline(highScores[index].name, MAX_NAME_SIZE, '\n');
cout << "Enter the score for score #" << (index + 1) << ": ";
cin >> highScores[index].score;
cin.ignore();
}
cout << endl;
}
void sortData(Highscore highScores[], int numItems) {
for (int count = 0; count < numItems - 1; count++){
swap(highScores[findIndexOfLargest(highScores, count, numItems)],
highScores[count]);
}
}
int findIndexOfLargest(const Highscore highScores[], int startingIndex, int numItems){
int indexOfLargest = startingIndex;
for (int count = startingIndex + 1; count < numItems; count++){
if (highScores[count].score > highScores[indexOfLargest].score){
indexOfLargest = count;
}
}
return indexOfLargest;
}
void displayData(const Highscore highScores[], int size)
{
cout << "Top Scorers: " << endl;
for(int index = 0; index < size; index++)
{
cout << highScores[index].name << ": " << highScores[index].score << endl;
}
}

Answer 1

You maybe looking for one of two things.
If you want to add something to a vector, the function is push_back
vecScores.push_back(value) ; //in a for loop.
https://www.cplusplus.com/reference/vector/vector/push_back/
If you want to add something to a map, you could just use the form of
mapScore[index]=value ; // in a for loop.
https://www.cplusplus.com/reference/map/map/operator[]/

Answer 2

Probably your professor wants you to write something like this:
void readData(std::vector<Highscore>& highScores)
{
for (auto it = highScores.begin(); it != highScores.end(); ++it) {
cout << "Enter the name for score #" << std::distance(highScores.begin(), it) << ": ";
cin.getline(it->name, MAX_NAME_SIZE, '\n');
cout << "Enter the score for score #" << std::distance(highScores.begin(), it) << ": ";
cin >> it->score;
cin.ignore();
}
cout << endl;
}
where it is the iterator that's incremented via ++it from highScores.begin() to just before highScores.end(); then you access the members of the highScores's element "pointed by" it via it->member.
Here's a complete demo.
By the way, considering how much your professor likes void(some_type&) functions (and using namespace std;, if that was not your own idea), I would doubt you have much to learn from him. You better buy a good book.

Answer 3

I would do it like this, also get used to typing std::
Why is "using namespace std;" considered bad practice?
Also be careful with signed/unsigned, be precise about it.
If something can't have a negative value use unsigned types (or size_t)
#include <iostream>
#include <string>
#include <vector>
struct HighScore
{
std::string name;
unsigned int score;
};
// use size_t for sizes (value will always >0)
std::vector<HighScore> GetHighScores(size_t size)
{
std::vector<HighScore> highScores;
std::string points;
for (size_t index = 0; index < size; index++)
{
HighScore score;
std::cout << "Enter the name for score #" << (index + 1) << ": ";
std::cin >> score.name;
std::cout << "Enter the score for score #" << (index + 1) << ": ";
std::cin >> points;
// convert string to int
score.score = static_cast<unsigned int>(std::atoi(points.c_str()));
highScores.push_back(score);
}
std::cout << std::endl;
return highScores;
}
int main()
{
auto highScores = GetHighScores(3);
return 1;
}