C++ Basic Program Runtime Error - c++

Question

I am writing a very easy program for the open.kattis programming website. This is one of the easiest problems on their website so its quite a hit to my ego. When I test the code myself it works fine, but their results indicate that I get a runtime error on an unknown test case. The link to the problem description is: https://open.kattis.com/problems/everywhere but the general basis of the problem is I'm trying to determine the number of unique instances in a list of strings
My code is:
#include <iostream>
#include <string.h>
using namespace std;
int main()
{
short t; // test cases
short trips;
char city[21];
char cities[50][21];
bool found;
short count;
// read in the number of test cases
cin >> t;
// loop through each test case
for(int i=0; i<t; i++)
{
// read in the number of trips taken
cin >> trips;
// reset the count to 0
count = 0;
// loop through each trip
for(int j=0; j<trips; j++)
{
// read in the city
cin >> city;
// Linear search to determine if city has been visited
found = false;
for(int k=0; k<count; k++)
{
if(strcmp(city, cities[k]) == 0)
found = true;
}
// If city hasn't been visted, increment count and add to list
if(!found)
{
strcpy(cities[count], city);
count++;
}
}
// Output results for test case
cout << count << endl;
}
return 0;
}

Answer 1

You misread the description. char cities[50][21] isn't enough for this exercise:
The number of trips is at most 100 and no city name contains more than 20 characters.
Calling the number of possible cities "trips" is a little bit misleading here, but it's not the number of tests (T ≤ 50). That being said, you could improve your program a lot if you separate the concerns and actually use the C++ standard library:
#include <iostream>
#include <set> // <- Hint: those both will help you tremendously!
#include <string> // <-
int single_test_case(){
// ...
}
int main(){
int tests;
std::cin >> tests;
for(int i = 0; i < tests; ++i){
std::cout << single_test_case();
}
return 0;
}