More appropriate way to loop input from a file? - c++

Question

I want to be able to loop this file opening and closing to continually search for names.
The first time is no problem and output is what is expected then, when choosing y for yes, an output loop occurs.
Any ideas as to why this would happen? The logic seems more than correct.
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
string boys, girls, name;
int rank;
char end = 'n';
while (end != 'y' || end != 'Y')
{
cout << "Enter a name to search";
cin >> name;
ifstream input;
input.open("Names2016");
if (input.fail())
cout << "Failed to open file.\n";
while (!input.eof())
{
input >> rank >> boys >> girls;
if (boys == name)
cout << name << " ranks " << rank << " among boys.\n";
if (girls == name)
cout << name << " ranks " << rank << " among girls.\n";
}
input.close();
cout << "Would you like to search another name?\n"
<< "Enter Y for yes or N for no.\n";
cin >> end;
}
return 0;
}

Answer 1

There are a some of things you can do to make this code better,
The first is to use ifstreams and do file input/output the proper idiomatic way in a loop, don't use .eof() to check for end of file in a loop condition (the answer linked in the comments is a good place to start if you want to know why),
The second thing you want to check for validity of the file with a simple if (!file) its much cleaner IMO.
The third thing is, when you have a local file handle like you do in your code, then you can just let it go out of scope and let the destructor cleanup the file and close() it, it's the C++ RAII way of doing things (notice that I have removed the open() method to the constructor call (which does the same thing)
Use cerr instead of cout to report errors
Use char instead of int to represent characters
Not a big change, but using std::toupper like advised in the other answer's comments is a good readable way to check for uppercase and lowercase values at the same time
#include <iostream>
#include <fstream>
#include <string>
#include <cctype>
using namespace std;
int main()
{
string boys, girls, name;
int rank;
char end = 'n';
while (std::toupper(end) == 'Y')
{
cout << "Enter a name to search";
cin >> name;
ifstream input{"Names2016"};
// change here
if (!input) {
cerr << "Failed to open file.\n";
}
while (input >> rank >> boys >> girls)
{
if (boys == name)
cout << name << " ranks " << rank << " among boys.\n";
if (girls == name)
cout << name << " ranks " << rank << " among girls.\n";
}
// change below, just let the file handle go out of scope and close
// input.close();
cout << "Would you like to search another name?\n"
<< "Enter Y for yes or N for no.\n";
cin >> end;
}
return 0;
}
But you can do better on the I/O if your file isn't guaranteed to change over different iterations (in which case you probably need to make sure that there is no race anyway, so I am assuming the file does not change much). Read in the file once and save that information to be used later
#include <iostream>
#include <fstream>
#include <string>
#include <cctype>
#include <unordered_map>
#include <vector>
using namespace std;
int main()
{
string boys_name, girls_name, name;
int rank;
char end = 'n';
ifstream input{"Names2016"};
if (!input) {
cerr << "Failed to open file" << endl;
}
// preprocess the information and store it in a map
// making a map from string to vector because it is unclear whether
// there is a 1-1 mapping from the name to the rank for each name
unordered_map<string, vector<int>> boys;
unordered_map<string, vector<int>> girls;
while (input >> rank >> boys_name >> girls_name) {
boys[boys_name].push_back(rank);
girls[girls_name].push_back(rank);
}
while (std::toupper(end) == 'Y')
{
cout << "Enter a name to search";
cin >> name;
// use the map to do the lookup, much faster than reading
// the entire file over and over again
}
return 0;
}

Answer 2

First of all, what is this supposed to mean int end = 'n'; Are you assigning an integer with a character value?!
And why are you opening the same file inside the loop. You should probably open it only once at the beginning of the program.
And the eof doesn't have what to check for, because you have to read from a file to reach its end.