how to compare strings in vector in c++? - c++

Question

hey I have class containing
#include <iostream>
#include <string>
#include <vector>
#include <fstream>
#include <iomanip>
using namespace std;
struct student
{
std::string ID;
std::string Name;
std::vector<std::string> friends;
};
And main function contains
int main() {
vector<student> List_Students = { { "d123", "Jacob", {"e321"} }, { "e321", "Abo", {"d123", "e456"} }, { "e456","Mark",{} } };
for (auto& s : List_Students)
{
cout << s.ID << "\t" << s.Name;
for (auto& f : s.friends)
{
cout << " " << f << " ";
}
cout << endl;
}
}
this yields output as expected
output:
d123 Jacob e321
e321 Abo d123 e456
e456 Mark
my question is how can I compare the vector of friends with IDs so that so that after it shows friends it shows their names with it. Expected output:
d123 Jacob e321 (Abo)
e321 Abo d123 (Jacob) e456 (Mark)
e456 Mark (No friends)
quite new to c++ any help would be appreciated thank you

Answer 1

You can use the standard std::find_if() algorithm, eg
...
#include <algorithm>
...
int main() {
vector<student> List_Students = {
{ "d123", "Jacob", {"e321"} },
{ "e321", "Abo", {"d123", "e456"} },
{ "e456", "Mark", {} }
};
for (auto& s : List_Students)
{
cout << s.ID << "\t" << s.Name;
if (s.friends.empty())
{
cout << " (No friends)";
}
else
{
for (auto& f : s.friends)
{
cout << " " << f << " ";
auto iter = find_if(List_Students.begin(), List_Students.end(),
[&](const student &s2){ return s2.ID == f; }
);
if (iter != List_Students.end())
{
cout << "(" << iter->Name << ") ";
}
}
}
cout << endl;
}
}
Or, like #Ch3steR said in comments, you can store the names in a std::map:
...
#include <map>
#include <utility>
...
int main() {
vector<student> List_Students = {
{ "d123", "Jacob", {"e321"} },
{ "e321", "Abo", {"d123", "e456"} },
{ "e456", "Mark", {} }
};
map<string, string> names;
for (auto& s : List_Students)
{
names.insert(make_pair(s.ID, s.Name));
}
for (auto& s : List_Students)
{
cout << s.ID << "\t" << s.Name;
if (s.friends.empty())
{
cout << " (No friends)";
}
else
{
for (auto& f : s.friends)
{
cout << " " << f << " (" << names[f] << ") ";
}
}
cout << endl;
}
}
Alternatively:
#include <iostream>
#include <string>
#include <map>
using namespace std;
struct student
{
string Name;
vector<string> friends;
};
int main() {
map<string, student> List_Students = {
{ "d123", { "Jacob", {"e321"} } },
{ "e321", { "Abo", {"d123", "e456"} } },
{ "e456", { "Mark", {} } }
};
for (auto& elem : List_Students)
{
auto &s = elem.second;
cout << elem.first << "\t" << s.Name;
if (s.friends.empty())
{
cout << " (No friends)";
}
else
{
for (auto& f : s.friends)
{
cout << " " << f << " (" << List_Students[f].Name << ") ";
}
}
cout << endl;
}
}